MATLAB: Do I receive different results from the DIFF function with char inputs between MATLAB 7.0 (R14) and MATLAB 6.5.1 (R13SP1)

answerchardiff()differentdoubler14symbolicSymbolic Math Toolboxwrong

For example, if I have the Symbolic Math Toolbox, and I execute the following command within MATLAB 6.5.1 (R13SP1):

diff('x^2')

I receive the expected result:

 ans = 
   2*x

However, in MATLAB 7.0 (R14), I receive the unexpected result:

 ans =
 -26   -44

Best Answer

This bug has been fixed for Release 14 SP1 (R14SP1). For previous releases, please read below for any possible workarounds:

This has been verified as a bug within MATLAB 7.0 (R14) in the way some functions that are overloaded for char inputs convert the inputs to double precision values rather than symbolic expressions.

Currently, to work around this issue, convert your char expressions to symbolic expressions prior to supplying them to the DIFF function.

Related Solutions

MATLAB: Do I receive different results when running the POLY2SYM function in the Symbolic Math Toolbox 3.1.2 (R14SP2)

This bug has been fixed in Release 2007b (R2007b). For previous product releases, read below for any possible workarounds:

There is a bug in the Symbolic Math Toolbox 3.1.2 (R14SP2) in the way that POLY2SYM handles imaginary numbers when MATLAB first starts, or after the "clear all" command is issued.

To work around this issue, enter the following command before calling POLY2SYM for the first time:

sym('i')

MATLAB: Do the ATAN2 and ANGLE functions in MATLAB 7.0 (R14) return different results from those in MATLAB 6.5.1 (R13SP1)

This bug has been fixed in MATLAB 7.0.1 (R14SP1). For previous releases, read below for any possible workarounds:

This is due to a change in the way that the ATAN2 and ANGLE functions handle the special case of "negative zero" inputs in MATLAB 7.0 (R14).

To receive the same answers as in R13SP1, explicitly hardcode the output to zero for cases where both input arguments to ATAN2 are zero:

a = [5 4 0 -4];
b = [6 3 -0 2];
x=atan2(a,b);
x(a==0 & b==0) = 0;

Best Answer

Related Solutions

MATLAB: Do I receive different results when running the POLY2SYM function in the Symbolic Math Toolbox 3.1.2 (R14SP2)

MATLAB: Do the ATAN2 and ANGLE functions in MATLAB 7.0 (R14) return different results from those in MATLAB 6.5.1 (R13SP1)

Related Question