Bug in symbolic toolbox?
1 view (last 30 days)
Show older comments
Hi all, I am experiencing a strange behavior of the sym function. The result of sym('I') is 'I'. While the result of sym('A+I') is 'A+i' with an unwanted lower case letter of 'I'.
Has anyone experienced such a behavior? Is it a bug? and if so is there any workaround?
Thanks, Junior
0 Comments
Accepted Answer
Walter Roberson
on 18 Aug 2011
In the input regions MuPAD recognizes an uppercase I as the imaginary unit (-1)^(1/2). In the output regions, MuPAD uses a lowercase i to display the imaginary unit
I – imaginary unit sqrt(-1) (see DOM_COMPLEX for details)
Complex numbers can be constructed by typing in the corresponding expression, such as 3+4*I. The keyword for typing the imaginary unit I is I (a capital letter i).
Thus, what you are seeing is not a bug.
I know that in Maple it is possible to change the representation letter, but I do not at the moment see any corresponding mechanism in MuPad. (In Maple, it would be by using interface(imaginaryunit=SYMBOL) )
More Answers (1)
Sean de Wolski
on 18 Aug 2011
It's seeing I as the sqrt(-1). What is your goal by doing it this way?
why not just
syms A I
A+I
?
The other easiest workaround would just be to use a different letter, J, or II.
sym('A+II')
5 Comments
Walter Roberson
on 18 Aug 2011
MuPad allows variable names that are not valid MATLAB variable names, so as long as you are processing at the MuPAD level, you could, for example, replace I by _I and strip off the underscore later.
Or.... http://www.mathworks.com/help/toolbox/mupad/datatypes/DOM_IDENT.html#DOM_IDENT
Additionally, an arbitrary string of characters enclosed in ‘backticks’ `` is also an identifier. Examples: `x+y`, `a plus 1`. If the string of characters between the back ticks is a valid identifier already, this input form creates the same identifier as the one without the backticks.
Thus, you could substitute (say) `I ` (with a space) where you have the variable I in your input, and the only visible difference with normal typesetting turned on would be an extra space after the I .
See Also
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!