using hasSymType(expression, 'constants') returns true when no constants
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When trying to find if my expression has constants, hasSymType() always returns true. For example
syms s;
hasSymType(s*2,'constant')
returns true.
children() seems to separate out the terms into it's components as well. I would expect the following code to return [s*2] but it returns [s 2].
syms s;
children(s*2)
What am I missing?
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Accepted Answer
Paul
on 29 Sep 2023
Hi Andrew,
Both of those examples seem to be in accordance with doc hasSymType and children, except that children returns a cell array, not an array of sym.
syms s
hasSymType(s*2,'constant')
syms s
children(s*2)
What is the reason expect different results?
More Answers (1)
Walter Roberson
on 29 Sep 2023
Internally, inside the symbolic engine, s*2 is coded as a data structure
_mult(DOM_IDENT('s'), DOM_INT(2))
and taking children() of that strips off the
_mult
layer, resulting in the multiple outputs DOM_IDENT('s') and DOM_INT(2) . The interface layer knows to wrap the multiple outputs into a cell array. So the output is {s sym(2)}
2*s is not an atomic entity: it is an expression that can be decomposed into its parts. One of those parts is a constant, which is why hasType() succeeds.
4 Comments
Walter Roberson
on 29 Sep 2023
Moved: Walter Roberson
on 29 Sep 2023
In the case where all of the coefficients are numeric (or convertable to double) you can use sym2poly and then look at the last entry.
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