4

I have looked up here how to declare recurrence equations.

I tried the following example from that page:

>> solve(rec(y(n + 1) = 3*(n + 1)*y(n), y(n), {y(0) = 1}))
                      |
Error: The expression to the left of the equals sign is not a valid target for an assignment.

Then I noticed that I didn't have the Symbolic Math Toolbox installed. After the installation 

>> ver

returned (among some others):

MATLAB                                                Version 8.1        (R2013a)
Symbolic Math Toolbox                                 Version 5.10       (R2013a)

but I still got the above error.

I could narrow the command down to the following, giving the same above error:

>> rec(y(n + 1) = y(n), y(n), {y(0) = 1})
                |
Error: The expression to the left of the equals sign is not a valid target for an assignment.

On the wiki and other google results, the error is only mentioned with a error when confusing = with ==.

Mohsen Nosratinia
  • 9,844
  • 1
  • 27
  • 52
typ1232
  • 5,535
  • 6
  • 35
  • 51

1 Answers1

5

rec is not a native Symbolic Toolbox function. It belongs to MuPAD which is a separate package that Mathworks acquired and added to Symbolic Toolbox. To use it you need to first enter mupad command in command window then you enter the command that uses rec in MuPAD window that pops up.

Mohsen Nosratinia
  • 9,844
  • 1
  • 27
  • 52
  • 1
    You can also evaluate MuPAD expressions from within MATLAB using `evalin(symengine, '...')`: http://www.mathworks.com/help/symbolic/evalin.html – Amro Sep 04 '13 at 19:16