Problems in for loop with risetime: Signal processing toolbox

I'm trying to calculate the rise time of 10000 pulses given as a matrix of size 80x10000.

I have tried to use the function "risetime" from signal processing toolbox. For calculation I use this code:

for k=1:size(PS1,2)
    PS2(:,k) = risetime(PS1(:,k),80);
end

As a result I get the error message: In an assignment A(:) = B, the number of elements in A and B must be the same.

The resulting matrix PS2 is of size 1x1011 but it should have 1x10000.

What is the problem?

[Jan]

How could you get a size for the resulting matrix, if the code stops with an error?

[toka55]

I get the error message and a resulting matrix but the matrix is not complete. Meantime, I realised that I get sometimes two values out of one pulse and then the matrix dimensions dosen't fit anymore. Any suggestions ?