Hi, I've been having some difficulty with Matlab. I keep getting confused with the indexing and the loops. To set up the code, I am trying to implement the ADI method for a 2-D heat equation (u_t=u_xx+u_yy+f(x,y,t)). I have Dirichlet boundary conditions on the left, upper, and lower boundaries, and a mixed boundary condition on the right boundary. The coefficient matrix and source vector look okay after the x-direction loop. I have spent well over a 10 hours trying to get it to work. Can somebody check the code please? Here's the code: http://docs.google.com/Doc?docid=0AS848wqcdh80ZHE0Njk2a18xMjZnN3I2cG1kaw&hl=en f, robinbc, and uexact are obtained from separate script files. Thank you.