subs command does not create symbolic variable?

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nafis irtija
nafis irtija 2015-6-19
评论： John D'Errico 2015-6-19
I am using MATLAB R2011a. I have symbolic math toolbox installed. When I use the "subs" command to replace a value in a symbolic variable, instead of symbolic variable a normal variable is created ... My code is
>> f=int(g,x)
f =
asin((2*x)/5 - 4/5)/2
>> subs (f,x,3)
ans =
0.2058
What am missing?
  2 个评论
nafis irtija
nafis irtija 2015-6-19
In the mathworks tutorial video they wrote
>>f3=subs(f,x,3)
and the variable f3 was symbolic.when i write the same code,f3 is not symbolic.and they used "eval(f3)" to get the value 0.2058.when I write
eval(f3)
it gives an error.
John D'Errico
John D'Errico 2015-6-19
It is difficult to know, since your version is so old. It works fine for me. For eample, since I do not have g, I did this:
syms x
f = asin((2*x)/5 - 4/5)/2
f =
asin((2*x)/5 - 4/5)/2
subs(f,x,3)
ans =
asin(2/5)/2
with no problems. But I am using the current release.

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回答（1 个）

Martin Brown
Martin Brown 2015-6-19
You've evaluated
asin((2*3)/5 - 4/5)/2
which is indeed 0.2058. It's no longer symbolic?

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