I am a bit confused by your question, as x is not defined. If you want to run your algorithim for a set number of randomly generated matrices and vectors then something similar to the code below should work:
numIterations = 10; % Number of random samples of your matrix / vector combo you want to compute
for Iteration = 1:numIterations
A = rand(100,100);
b = rand(100,1);
x = myLeastSquareAlgo(A,b); % Your algorithim function that calculates 'x'.
normArray(Iteration) = norm(b-A*x);
end
meanNorm = mean(normArray);
