[function] MATLAB error: Undefined function or method X for input arguments of type 'double'

The most common cause of this problem is that Matlab cannot find the file on it's search path. Basically, Matlab looks for files in:

  1. The current directory (pwd);
  2. Directly in a directory on the path (to see the path, type path at the command line)
  3. In a directory named @(whatever the class of the first argument is) that is in any directory above.

    As someone else suggested, you can use the command which, but that is often unhelpful in this case - it tells you Matlab can't find the file, which you knew already.

    So the first thing to do is make sure the file is locatable on the path.

    Next thing to do is make sure that the file that matlab is finding (use which) requires the same type as the first argument you are actually passing. I.el, If w is supposed to be different class, and there is a divrat function there, but w is actually empty, [], so matlab is looking for Double/divrat, when there is only a @(yourclass)/divrat. This is just speculation on my part, but this often bites me.