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How to substitute multiple values in symbolic matrix?

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Amit Kumar
Amit Kumar 2013-11-29
评论： Youssef El Seblani ，2018-4-8
Hi, How to substitute multiple values in symbolic matrix? With function subs, we can substitute only single value in expression. Writing nested subs(subs(...)) can work but it becomes tedious. Here is sample code:
syms x y z w
N=[ 1y+y+z,x/2 - y/3 + z/3, x*y, x+z];
Is there any way to substitute values to w,x,y,z in single line? I guess then I have to define variables like x(1), x(2) etc. and have to use for loop to change values. Is this approach correct or is there any better way?

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Andrei Bobrov
Andrei Bobrov 2013-11-29
syms x y z w
N=[ w+y+z,x/2 - y/3 + z/3, x*y, x+z]
X = sym(['[',sprintf('X(%d) ',1:4),']'])
out = subs(N,[x, y, z, w],X)
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Karan Gill
Karan Gill 2016-12-8
That answer is wrong. Please do not use string input to sym. Instead:
>> syms x y z w
N=[ 1*y+y+z,x/2 - y/3 + z/3, x*y, x+z];
vars = [w x y z];
newVars = sym('x%d',[1 4]);
subs(N,vars,newVars)
ans =
[ 2*x3 + x4, x2/2 - x3/3 + x4/3, x2*x3, x2 + x4]
Much easier to read and understand. Look up the doc for sym to understand the command I used: https://www.mathworks.com/help/symbolic/sym.html

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Youssef El Seblani
Youssef El Seblani 2018-3-31
编辑：Walter Roberson 2018-3-31
clc
clear
syms x y z w
N=[ w+y+z,x/2 - y/3 + z/3, x*y, x+z]
A=sym('X',[1,4])
N(A) = subs(N,[x, y, z, w],A)
for example
N(1,2,3,4)
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