matlab

Question

我有以下代码：

tic;
H = rand(100, 1000);
    F = rand(1, 1000);
    net = newff(H, F, [30, 10], { 'tansig' 'tansig'}, 'traingdx', 'learngdm', 'mse');

    net.trainParam.epochs = 400;
    net.performParam.regularization = 0.05;

    net.divideParam.trainRatio = 1;
    net.divideParam.valRatio = 0;
    net.divideParam.testRatio = 0;

    net.trainParam.showWindow = 0;
    net.trainParam.showCommandLine = 0;

    % net = train(net, H, F, 'useGPU', 'yes', 'showResources', 'yes'); % line 1
    net = train(net, H, F, 'showResources', 'yes'); % line 2

toc;

第2行未注释我得

Computing Resources:
GPU device #1, GeForce 800M

Elapsed time is 5.084222 seconds.

并且第1行未注释我得

Computing Resources:
MEX2

Elapsed time is 1.870803 seconds.

为什么GPU比CPU慢？ 我的GPU属性：

CUDADevice with properties:

                  Name: 'GeForce 800M'
                 Index: 1
     ComputeCapability: '2.1'
        SupportsDouble: 1
         DriverVersion: 6
        ToolkitVersion: 5
    MaxThreadsPerBlock: 1024
      MaxShmemPerBlock: 49152
    MaxThreadBlockSize: [1024 1024 64]
           MaxGridSize: [65535 65535 65535]
             SIMDWidth: 32
           TotalMemory: 2.1475e+09
            FreeMemory: 1.9886e+09
   MultiprocessorCount: 1
          ClockRateKHz: 1475000
           ComputeMode: 'Default'
  GPUOverlapsTransfers: 1
KernelExecutionTimeout: 1
      CanMapHostMemory: 1
       DeviceSupported: 1
        DeviceSelected: 1`