Strange behavior with subs (symbolic substitute)

Question

Lilllly 2015-6-25

回答： Sean de Wolski 2015-6-25

Hi,

I'm facing a strange problem when using subs (in MATLAB_R2015a)

The following example from the documentation works as it should:

subs(a*b^2, a*b, 5)
ans =
5*b

However, when I am trying slightly different substitutions, the term is not replaced as I would expect it (e.g. resulting in 25*a):

subs(a*b^4, b*b, 5)
ans =
a*b^4
subs(a*b*b*b*b, b*b, 5)
ans =
a*b^4

I'm sure I'm just overseeing something here, but I don't understand wha it doesn't work.

Thanks in advance!

Answer 1

Sean de Wolski 2015-6-25

You need to just specify which variable is being substituted and then do the value.

subs(a*b^4, b, sqrt(5))

And for more info.

doc subs