Matrix Dimensions Must Agree Error, Error using +

-2*(D2*(q_(1,:)'))-2*pr.*(f_(1,:)').*(D1*(q_(1,:)'))...
    +2*pr.*A*(D1*(f_(1,:)')).*((q_(1,:)'))-de.*pr.*((A*(f_(1,:)')).*(D2*(f_(1,:)')).*(q_(1,:)')...
    +A*(2*(size(x))+A)*((f_(1,:)').^2).*(q_(1,:)')+(eye(size(x))+2*A)*(f_(1,:)').*(D1*(f_(1,:)')).*(D1*(q_(1,:)'))-((f_(1,:)').^2).*(D2*(f_(1,:)')));

[Walter Roberson]

You have given us no information about the size() of each of the variables involved.

[mariam ahmad]

i get this error in first line

[the cyclist]

You are not giving us info to debug this directly. But I can give you some advice on how to debug it.

When you have a long line of code like this, try to separately evaluate small segments. Remove sections until the code runs, and then add them back in one-by-one. Try to isolate the piece that makes this break, in a systematic fashion.

[MHZ]

Mariam, We don't know the values for any of your variables, so we cannot reproduce the error. Can you put the full script please?

On a side note: you are switching between element and matrix multiplication (the dot ".") .* is element wise multiplication. * is matrix multiplication. I suggest you check that.