You have to define net before modifying any properties.
clear all, close all, clc
[x,t] = iris_dataset;
for i = 1:2
net = patternnet([]);
if i==1
net.divideFcn = '';
else
net.divideParam.trainRatio = 1;
net.divideParam.valRatio = 0;
net.divideParam.testRatio = 0;
end
net = train(net,x,t);
view(net)
y = net(x);
MSE(i) = mse(y-t)
end
MSE = 0.0084 0.0084
Hope this helps.
Greg