Throw an exception if the user requests double precision on a device that doesn't support it.

platforms/cuda/src/CudaContext.cpp

@@ -124,6 +124,8 @@ CudaContext::CudaContext(const System& system, int deviceIndex, bool useBlocking
     CHECK_RESULT(cuDeviceComputeCapability(&major, &minor, device));
     gpuArchitecture = intToString(major)+intToString(minor);
     computeCapability = major+0.1*minor;
+    if ((useDoublePrecision || useMixedPrecision) && computeCapability < 1.3)
+        throw OpenMMException("This device does not support double precision");
     defaultOptimizationOptions = "--use_fast_math";
     unsigned int flags = CU_CTX_MAP_HOST;
     if (useBlockingSync)

platforms/opencl/src/OpenCLContext.cpp

@@ -154,6 +154,8 @@ OpenCLContext::OpenCLContext(const System& system, int platformIndex, int device
 	        defaultOptimizationOptions = "-cl-fast-relaxed-math";
         supports64BitGlobalAtomics = (device.getInfo<CL_DEVICE_EXTENSIONS>().find("cl_khr_int64_base_atomics") != string::npos);
         supportsDoublePrecision = (device.getInfo<CL_DEVICE_EXTENSIONS>().find("cl_khr_fp64") != string::npos);
+        if ((useDoublePrecision || useMixedPrecision) && !supportsDoublePrecision)
+            throw OpenMMException("This device does not support double precision");
         string vendor = device.getInfo<CL_DEVICE_VENDOR>();
         int numThreadBlocksPerComputeUnit = 6;
         if (vendor.size() >= 6 && vendor.substr(0, 6) == "NVIDIA") {