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Starting with all symbols, ending with mixed symbols and number?

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Craig
Craig 2023-12-11
编辑： Dyuman Joshi 2023-12-11
I'm performing some symbolic manipulations that result in
(a/b)*x
I'd like to keep 'x' a symbol and substitute numbers for a and b. Unfortunately, the numbers are treated symbolically and a/b doesn't simplify
double((a/b)*x ) doesn't work because x is still a symbol. I'm sure there's a trivial solution that I haven't found.
thanks in advance

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采纳的回答

Walter Roberson
Walter Roberson 2023-12-11
Ran in:
syms a b x
%Expression
y = (a/b)*x;
newy0 = subs(y, [a b], [2 3])
newy0 = 
newy1 = subs(y, [a b], sym([2 3], 'd'))
newy1 = 
newy2 = vpa(subs(y, [a b], [2 3]))
newy2 = 
sympref('FloatingPointOutput', true)
ans = logical
0
newy4 = subs(y, [a b], [2 3])
newy4 = 

更多回答（2 个）

Dyuman Joshi
Dyuman Joshi 2023-12-11
编辑：Dyuman Joshi 2023-12-11
Ran in:
Use subs -
syms a b x
%Expression
y = (a/b)*x;
y = subs(y, [a b], [2 3])
y = 
If you want the expression in decimal representation, you could use vpa -
%Decimal representation with atleast 10 significant digits
y = vpa(y, 10)
y = 
Torsten
Torsten 2023-12-11
移动：Torsten 2023-12-11
Unfortunately, the numbers are treated symbolically and a/b doesn't simplify
The numbers are not treated symbolically, but as long as x is symbolic, the complete expression is symbolic.
"double" can only be applied to expressions in which all symbolic variables have been substituted by numerical values.

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