Merge pull request #1547 from peastman/paramderivs

Energy derivatives with respect to global parameters

docs-source/usersguide/theory.rst

@@ -1086,6 +1086,24 @@ is exactly equivalent to
 The definition of an intermediate value may itself involve other intermediate
 values.  All uses of a value must appear *before* that value’s definition.
 
+Parameter Derivatives
+*********************
+
+Many custom forces have the ability to compute derivatives of the potential energy
+with respect to global parameters.  To use this feature, first define a global
+parameter that the energy depends on.  Then instruct the custom force to compute
+the derivative with respect to that parameter by calling :meth:`addEnergyParameterDerivative()`
+on it.  Whenever forces and energies are computed, the specified derivative will
+then also be computed at the same time.  You can query it by calling :meth:`getState()`
+on a :class:`Context`, just as you would query forces or energies.
+
+An important application of this feature is to use it in combination with a
+:class:`CustomIntegrator` (described in section :ref:`custom-integrator`\ ).  The
+derivative can appear directly in expressions that define the integration
+algorithm.  This can be used to implement algorithms such as lambda-dynamics,
+where a global parameter is integrated as a dynamic variable.
+
+
 Integrators
 ###########
 
@@ -1235,6 +1253,8 @@ Furthermore, because Langevin dynamics involves a random force, it can never be
 symplectic and therefore the fixed step size Verlet integrator’s advantages do
 not apply to the Langevin integrator.
 
+.. _custom-integrator:
+
 CustomIntegrator
 ****************
 

libraries/lepton/include/lepton/CustomFunction.h

@@ -48,7 +48,7 @@ public:
     virtual ~CustomFunction() {
     }
     /**
-     * Get the number of arguments this function exprects.
+     * Get the number of arguments this function expects.
      */
     virtual int getNumArguments() const = 0;
     /**

libraries/lepton/src/ParsedExpression.cpp

@@ -109,7 +109,7 @@ ExpressionTreeNode ParsedExpression::precalculateConstantSubexpressions(const Ex
     for (int i = 0; i < (int) children.size(); i++)
         children[i] = precalculateConstantSubexpressions(node.getChildren()[i]);
     ExpressionTreeNode result = ExpressionTreeNode(node.getOperation().clone(), children);
-    if (node.getOperation().getId() == Operation::VARIABLE)
+    if (node.getOperation().getId() == Operation::VARIABLE || node.getOperation().getId() == Operation::CUSTOM)
         return result;
     for (int i = 0; i < (int) children.size(); i++)
         if (children[i].getOperation().getId() != Operation::CONSTANT)

olla/include/openmm/kernels.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008-2015 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -172,6 +172,12 @@ public:
      * @param forces  on exit, this contains the forces
      */
     virtual void getForces(ContextImpl& context, std::vector<Vec3>& forces) = 0;
+    /**
+     * Get the current derivatives of the energy with respect to context parameters.
+     *
+     * @param derivs  on exit, this contains the derivatives
+     */
+    virtual void getEnergyParameterDerivatives(ContextImpl& context, std::map<std::string, double>& derivs) = 0;
     /**
      * Get the current periodic box vectors.
      *

openmmapi/include/openmm/CustomAngleForce.h

@@ -64,6 +64,10 @@ namespace OpenMM {
  * force->addPerAngleParameter("theta0");
  * </pre></tt>
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -97,6 +101,13 @@ public:
     int getNumGlobalParameters() const {
         return globalParameters.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the algebraic expression that gives the interaction energy for each angle
      */
@@ -162,6 +173,21 @@ public:
      * @param defaultValue   the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add an angle term to the force field.
      *
@@ -225,6 +251,7 @@ private:
     std::vector<AngleParameterInfo> parameters;
     std::vector<GlobalParameterInfo> globalParameters;
     std::vector<AngleInfo> angles;
+    std::vector<int> energyParameterDerivatives;
     bool usePeriodic;
 };
 

openmmapi/include/openmm/CustomBondForce.h

@@ -64,6 +64,10 @@ namespace OpenMM {
  * force->addPerBondParameter("r0");
  * </pre></tt>
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -97,6 +101,13 @@ public:
     int getNumGlobalParameters() const {
         return globalParameters.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the algebraic expression that gives the interaction energy for each bond
      */
@@ -162,6 +173,21 @@ public:
      * @param defaultValue   the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add a bond term to the force field.
      *
@@ -222,6 +248,7 @@ private:
     std::vector<BondParameterInfo> parameters;
     std::vector<GlobalParameterInfo> globalParameters;
     std::vector<BondInfo> bonds;
+    std::vector<int> energyParameterDerivatives;
     bool usePeriodic;
 };
 

openmmapi/include/openmm/CustomCentroidBondForce.h

@@ -99,6 +99,10 @@ namespace OpenMM {
  * force->addBond(bondGroups, bondParameters);
  * </pre></tt>
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -150,6 +154,13 @@ public:
     int getNumGlobalParameters() const {
         return globalParameters.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the number of tabulated functions that have been defined.
      */
@@ -229,6 +240,21 @@ public:
      * @param defaultValue   the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add a particle group.
      *
@@ -351,6 +377,7 @@ private:
     std::vector<GroupInfo> groups;
     std::vector<BondInfo> bonds;
     std::vector<FunctionInfo> functions;
+    std::vector<int> energyParameterDerivatives;
     bool usePeriodic;
 };
 

openmmapi/include/openmm/CustomCompoundBondForce.h

@@ -88,6 +88,10 @@ namespace OpenMM {
  * force->addPerBondParameter("r0");
  * </pre></tt>
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -133,6 +137,13 @@ public:
     int getNumGlobalParameters() const {
         return globalParameters.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the number of tabulated functions that have been defined.
      */
@@ -212,6 +223,21 @@ public:
      * @param defaultValue   the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add a bond to the force
      *
@@ -323,6 +349,7 @@ private:
     std::vector<GlobalParameterInfo> globalParameters;
     std::vector<BondInfo> bonds;
     std::vector<FunctionInfo> functions;
+    std::vector<int> energyParameterDerivatives;
     bool usePeriodic;
 };
 

openmmapi/include/openmm/CustomGBForce.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008-2014 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -128,6 +128,10 @@ namespace OpenMM {
  * however, you can use the computation type ParticlePairNoExclusions to indicate that exclusions should not be applied to a
  * particular piece of the computation.
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -207,6 +211,13 @@ public:
     int getNumGlobalParameters() const {
         return globalParameters.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the number of tabulated functions that have been defined.
      */
@@ -312,6 +323,21 @@ public:
      * @param defaultValue  the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add the nonbonded force parameters for a particle.  This should be called once for each particle
      * in the System.  When it is called for the i'th time, it specifies the parameters for the i'th particle.
@@ -550,6 +576,7 @@ private:
     std::vector<FunctionInfo> functions;
     std::vector<ComputationInfo> computedValues;
     std::vector<ComputationInfo> energyTerms;
+    std::vector<int> energyParameterDerivatives;
 };
 
 /**

openmmapi/include/openmm/CustomIntegrator.h

@@ -202,6 +202,16 @@ namespace OpenMM {
  * following comparison operators: =, <. >, !=, <=, >=.  Blocks may be nested
  * inside each other.
  * 
+ * Another feature of CustomIntegrator is that it can use derivatives of the
+ * potential energy with respect to context parameters.  These derivatives are
+ * typically computed by custom forces, and are only computed if a Force object
+ * has been specifically told to compute them by calling addEnergyParameterDerivative()
+ * on it.  CustomIntegrator provides a deriv() function for accessing these
+ * derivatives in global or per-DOF expressions.  For example, "deriv(energy, lambda)"
+ * is the derivative of the total potentially energy with respect to the parameter
+ * lambda.  You can also restrict it to a single force group by specifying a different
+ * variable for the first argument, such as "deriv(energy1, lambda)".
+ *
  * An Integrator has one other job in addition to evolving the equations of motion:
  * it defines how to compute the kinetic energy of the system.  Depending on the
  * integration method used, simply summing mv<sup>2</sup>/2 over all degrees of

openmmapi/include/openmm/CustomNonbondedForce.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008-2014 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -119,6 +119,10 @@ namespace OpenMM {
  * (or when you modify per-particle parameters by calling updateParametersInContext()).  This means that if parameters change
  * frequently, the long range correction can be very slow.  For this reason, it is disabled by default.
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -204,6 +208,13 @@ public:
     int getNumInteractionGroups() const {
         return interactionGroups.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the algebraic expression that gives the interaction energy between two particles
      */
@@ -321,6 +332,21 @@ public:
      * @param defaultValue   the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add the nonbonded force parameters for a particle.  This should be called once for each particle
      * in the System.  When it is called for the i'th time, it specifies the parameters for the i'th particle.
@@ -494,6 +520,7 @@ private:
     std::vector<ExclusionInfo> exclusions;
     std::vector<FunctionInfo> functions;
     std::vector<InteractionGroupInfo> interactionGroups;
+    std::vector<int> energyParameterDerivatives;
 };
 
 /**

openmmapi/include/openmm/CustomTorsionForce.h

@@ -64,6 +64,10 @@ namespace OpenMM {
  * force->addPerTorsionParameter("theta0");
  * </pre></tt>
  * 
+ * This class also has the ability to compute derivatives of the potential energy with respect to global parameters.
+ * Call addEnergyParameterDerivative() to request that the derivative with respect to a particular parameter be
+ * computed.  You can then query its value in a Context by calling getState() on it.
+ *
  * Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following
  * functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, floor, ceil, step, delta, select.  All trigonometric functions
  * are defined in radians, and log is the natural logarithm.  step(x) = 0 if x is less than 0, 1 otherwise.  delta(x) = 1 if x is 0, 0 otherwise.
@@ -97,6 +101,13 @@ public:
     int getNumGlobalParameters() const {
         return globalParameters.size();
     }
+    /**
+     * Get the number of global parameters with respect to which the derivative of the energy
+     * should be computed.
+     */
+    int getNumEnergyParameterDerivatives() const {
+        return energyParameterDerivatives.size();
+    }
     /**
      * Get the algebraic expression that gives the interaction energy for each torsion
      */
@@ -162,6 +173,21 @@ public:
      * @param defaultValue   the default value of the parameter
      */
     void setGlobalParameterDefaultValue(int index, double defaultValue);
+    /**
+     * Request that this Force compute the derivative of its energy with respect to a global parameter.
+     * The parameter must have already been added with addGlobalParameter().
+     *
+     * @param name             the name of the parameter
+     */
+    void addEnergyParameterDerivative(const std::string& name);
+    /**
+     * Get the name of a global parameter with respect to which this Force should compute the
+     * derivative of the energy.
+     *
+     * @param index     the index of the parameter derivative, between 0 and getNumEnergyParameterDerivatives()
+     * @return the parameter name
+     */
+    const std::string& getEnergyParameterDerivativeName(int index) const;
     /**
      * Add a torsion term to the force field.
      *
@@ -228,6 +254,7 @@ private:
     std::vector<TorsionParameterInfo> parameters;
     std::vector<GlobalParameterInfo> globalParameters;
     std::vector<TorsionInfo> torsions;
+    std::vector<int> energyParameterDerivatives;
     bool usePeriodic;
 };
 

openmmapi/include/openmm/State.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008 Stanford University and the Authors.           *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -58,7 +58,7 @@ public:
      * This is an enumeration of the types of data which may be stored in a State.  When you create
      * a State, use these values to specify which data types it should contain.
      */
-    enum DataType {Positions=1, Velocities=2, Forces=4, Energy=8, Parameters=16};
+    enum DataType {Positions=1, Velocities=2, Forces=4, Energy=8, Parameters=16, ParameterDerivatives=32};
     /**
      * Construct an empty State containing no data.  This exists so State objects can be used in STL containers.
      */
@@ -108,6 +108,17 @@ public:
      * Get a map containing the values of all parameters.  If this State does not contain parameters, this will throw an exception.
      */
     const std::map<std::string, double>& getParameters() const;
+    /**
+     * Get a map containing derivatives of the potential energy with respect to context parameters.
+     * In most cases derivatives are only calculated if the corresponding Force objects have been
+     * specifically told to compute them.  Otherwise, the values in the map will be zero.  Likewise,
+     * if multiple Forces depend on the same parameter but only some have been told to compute
+     * derivatives with respect to it, the returned value will include only the contributions from
+     * the Forces that were told to compute it.
+     * 
+     * If this State does not contain parameter derivatives, this will throw an exception.
+     */
+    const std::map<std::string, double>& getEnergyParameterDerivatives() const;
     /**
      * Get which data types are stored in this State.  The return value is a sum of DataType flags.
      */
@@ -118,6 +129,7 @@ private:
     void setVelocities(const std::vector<Vec3>& vel);
     void setForces(const std::vector<Vec3>& force);
     void setParameters(const std::map<std::string, double>& params);
+    void setEnergyParameterDerivatives(const std::map<std::string, double>& derivs);
     void setEnergy(double ke, double pe);
     void setPeriodicBoxVectors(const Vec3& a, const Vec3& b, const Vec3& c);
     int types;
@@ -126,7 +138,7 @@ private:
     std::vector<Vec3> velocities;
     std::vector<Vec3> forces;
     Vec3 periodicBoxVectors[3];
-    std::map<std::string, double> parameters;
+    std::map<std::string, double> parameters, energyParameterDerivatives;
 };
 
 /**
@@ -142,6 +154,7 @@ public:
     void setVelocities(const std::vector<Vec3>& vel);
     void setForces(const std::vector<Vec3>& force);
     void setParameters(const std::map<std::string, double>& params);
+    void setEnergyParameterDerivatives(const std::map<std::string, double>& params);
     void setEnergy(double ke, double pe);
     void setPeriodicBoxVectors(const Vec3& a, const Vec3& b, const Vec3& c);
 private:

openmmapi/include/openmm/internal/ContextImpl.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008-2013 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -138,6 +138,10 @@ public:
      * @param value the value of the parameter
      */
     void setParameter(std::string name, double value);
+    /**
+     * Get the derivatives of the energy with respect to parameters.
+     */
+    void getEnergyParameterDerivatives(std::map<std::string, double>& derivs);
     /**
      * Get the vectors defining the axes of the periodic box (measured in nm).  They will affect
      * any Force that uses periodic boundary conditions.

openmmapi/include/openmm/internal/CustomIntegratorUtilities.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2015 Stanford University and the Authors.           *
+ * Portions copyright (c) 2015-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -34,8 +34,10 @@
 
 #include "openmm/CustomIntegrator.h"
 #include "openmm/internal/ContextImpl.h"
+#include "lepton/CustomFunction.h"
 #include "lepton/ParsedExpression.h"
 #include <map>
+#include <string>
 #include <vector>
 
 namespace OpenMM {
@@ -48,6 +50,7 @@ class System;
 
 class OPENMM_EXPORT CustomIntegratorUtilities {
 public:
+    class DerivFunction;
     enum Comparison {
         EQUAL = 0, LESS_THAN = 1, GREATER_THAN = 2, NOT_EQUAL = 3, LESS_THAN_OR_EQUAL = 4, GREATER_THAN_OR_EQUAL = 5
     };
@@ -82,6 +85,28 @@ private:
             const std::vector<bool>& invalidatesForces, const std::vector<int>& forceGroup, std::vector<bool>& computeBoth);
     static void analyzeForceComputationsForPath(std::vector<int>& steps, const std::vector<bool>& needsForces, const std::vector<bool>& needsEnergy,
             const std::vector<bool>& invalidatesForces, const std::vector<int>& forceGroup, std::vector<bool>& computeBoth);
+    static void validateDerivatives(const Lepton::ExpressionTreeNode& node, const std::vector<std::string>& derivNames);
+};
+
+/**
+ * This class is used to implement the deriv() function when it appears in expressions.
+ */
+class CustomIntegratorUtilities::DerivFunction : public Lepton::CustomFunction {
+public:
+    DerivFunction() {
+    }
+    int getNumArguments() const {
+        return 2;
+    }
+    double evaluate(const double* arguments) const {
+        return 0.0;
+    }
+    double evaluateDerivative(const double* arguments, const int* derivOrder) const {
+        return 0.0;
+    }
+    CustomFunction* clone() const {
+        return new DerivFunction();
+    }
 };
 
 } // namespace OpenMM

openmmapi/include/openmm/internal/CustomNonbondedForceImpl.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008-2014 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -63,9 +63,10 @@ public:
     void updateParametersInContext(ContextImpl& context);
     /**
      * Compute the coefficient which, when divided by the periodic box volume, gives the
-     * long range correction to the energy.
+     * long range correction to the energy.  If the Force computes parameter derivatives,
+     * also compute the corresponding derivatives of the correction.
      */
-    static double calcLongRangeCorrection(const CustomNonbondedForce& force, const Context& context);
+    static void calcLongRangeCorrection(const CustomNonbondedForce& force, const Context& context, double& coefficient, std::vector<double>& derivatives);
 private:
     static double integrateInteraction(Lepton::CompiledExpression& expression, const std::vector<double>& params1, const std::vector<double>& params2,
             const CustomNonbondedForce& force, const Context& context);

openmmapi/src/Context.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2008-2015 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -84,8 +84,9 @@ State Context::getState(int types, bool enforcePeriodicBox, int groups) const {
     builder.setPeriodicBoxVectors(periodicBoxSize[0], periodicBoxSize[1], periodicBoxSize[2]);
     bool includeForces = types&State::Forces;
     bool includeEnergy = types&State::Energy;
-    if (includeForces || includeEnergy) {
-        double energy = impl->calcForcesAndEnergy(includeForces || includeEnergy, includeEnergy, groups);
+    bool includeParameterDerivs = types&State::ParameterDerivatives;
+    if (includeForces || includeEnergy || includeParameterDerivs) {
+        double energy = impl->calcForcesAndEnergy(includeForces || includeEnergy || includeParameterDerivs, includeEnergy, groups);
         if (includeEnergy)
             builder.setEnergy(impl->calcKineticEnergy(), energy);
         if (includeForces) {
@@ -100,6 +101,11 @@ State Context::getState(int types, bool enforcePeriodicBox, int groups) const {
             params[iter->first] = iter->second;
         builder.setParameters(params);
     }
+    if (types&State::ParameterDerivatives) {
+        map<string, double> derivs;
+        impl->getEnergyParameterDerivatives(derivs);
+        builder.setEnergyParameterDerivatives(derivs);
+    }
     if (types&State::Positions) {
         vector<Vec3> positions;
         impl->getPositions(positions);

openmmapi/src/ContextImpl.cpp

@@ -240,6 +240,10 @@ void ContextImpl::setParameter(std::string name, double value) {
     integrator.stateChanged(State::Parameters);
 }
 
+void ContextImpl::getEnergyParameterDerivatives(std::map<std::string, double>& derivs) {
+    updateStateDataKernel.getAs<UpdateStateDataKernel>().getEnergyParameterDerivatives(*this, derivs);
+}
+
 void ContextImpl::getPeriodicBoxVectors(Vec3& a, Vec3& b, Vec3& c) {
     updateStateDataKernel.getAs<UpdateStateDataKernel>().getPeriodicBoxVectors(*this, a, b, c);
 }

openmmapi/src/CustomAngleForce.cpp

@@ -95,6 +95,20 @@ void CustomAngleForce::setGlobalParameterDefaultValue(int index, double defaultV
     globalParameters[index].defaultValue = defaultValue;
 }
 
+void CustomAngleForce::addEnergyParameterDerivative(const string& name) {
+    for (int i = 0; i < globalParameters.size(); i++)
+        if (name == globalParameters[i].name) {
+            energyParameterDerivatives.push_back(i);
+            return;
+        }
+    throw OpenMMException(string("addEnergyParameterDerivative: Unknown global parameter '"+name+"'"));
+}
+
+const string& CustomAngleForce::getEnergyParameterDerivativeName(int index) const {
+    ASSERT_VALID_INDEX(index, energyParameterDerivatives);
+    return globalParameters[energyParameterDerivatives[index]].name;
+}
+
 int CustomAngleForce::addAngle(int particle1, int particle2, int particle3, const vector<double>& parameters) {
     angles.push_back(AngleInfo(particle1, particle2, particle3, parameters));
     return angles.size()-1;

openmmapi/src/CustomBondForce.cpp

@@ -95,6 +95,20 @@ void CustomBondForce::setGlobalParameterDefaultValue(int index, double defaultVa
     globalParameters[index].defaultValue = defaultValue;
 }
 
+void CustomBondForce::addEnergyParameterDerivative(const string& name) {
+    for (int i = 0; i < globalParameters.size(); i++)
+        if (name == globalParameters[i].name) {
+            energyParameterDerivatives.push_back(i);
+            return;
+        }
+    throw OpenMMException(string("addEnergyParameterDerivative: Unknown global parameter '"+name+"'"));
+}
+
+const string& CustomBondForce::getEnergyParameterDerivativeName(int index) const {
+    ASSERT_VALID_INDEX(index, energyParameterDerivatives);
+    return globalParameters[energyParameterDerivatives[index]].name;
+}
+
 int CustomBondForce::addBond(int particle1, int particle2, const vector<double>& parameters) {
     bonds.push_back(BondInfo(particle1, particle2, parameters));
     return bonds.size()-1;