machine learning - Testing The Trained Neural Network

i want use neural network classify handwritten digits of mnist dataset

i have created 2 layer neural network 100 hidden unit , trained using 60,000 * 784 trainimages matrix , 60,000 * 1 trainlabels

net = newff(trainimages,trainlabels,100)

how test , calculate error rate of trained network 10,000 * 784 testimages

training:

[net,tr]=train(net,trainimages',trainlabels');

testing:

predictedlabels = sim(net,testimages'); error_rate = 1- mean(predictedlabels == testlabels');

Test