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

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

Answer 1

[Walter Roberson]

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 = 

Answer 2

[Dyuman Joshi]

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 = 

Answer 3

[Torsten]

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.