Error in buit in function

i get error in built in function and i can't find out why and while trying to figure it out, i looked it up in the help and took the same example and then executed it in the command windows after trying the code i always get the same error ,but if cleared the work space and tried the example again before trying the code it works well it looks like the code make some thing wrong with the matlab *

[CS Researcher]

It works fine on my system. You have not made any function called double, right?

[Walter Roberson]

Yup, clearly they have created double.m and put it on their path.

[Mo BO]

yes i have,but how is that effecting the built in function.I did't even call it or use it in by code

Answer 1

[Walter Roberson]

When you created double.m in a local directory, and put the local directory on the path, that affected most calls to double(). MATLAB mostly finds appropriate routines by name: it usually starts at the beginning of the MATLAB path and looks for a double() in each directory until it finds one. It does not matter that the first routine you invoke does not call double(): that routine invokes another routine that does call double(), and the double.m that you put on the path now overrides the built-in double() routine.

You should not name your .m files the same as any Mathworks-provided routine unless you want your routine to be called instead of the Mathworks provided routine.

[Mo BO]

and that routine you mentioned is impeded in linspace,but not in all built in function so this error doesn't appear in all of my code ? did i get it right ?

[Walter Roberson]

http://www.mathworks.com/help/matlab/matlab_prog/function-precedence-order.html

[Mo BO]

ok,but why when i clear work space this problem is eliminated if i directly used the built in function in the command window and appear again in if tried it also in the command window but after executing the code ? and how i can know the names that matlab already use to avoid it

[Walter Roberson]

Your function might be changing the MATLAB path.

To see if any particular name is in use for a function, use

which TheNameToCheck

for example

which image
which doublefactorial

The second of those turns out not to be used (but there is a MuPAD double factorial function named fact2)