HELP. Symbolic substitution IN MATLAB. - 未名空间MITBBS历史存档

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HELP. Symbolic substitution IN MATLAB.

HELP. Symbolic substitution IN MATLAB.# Computation - 科学计算

o*l2004-07-23 07:07

1 楼

i need conversation between symbolic expression and numerical one frequently.
tried the command: subs(S,old,new). which can just substitute one specific
symbol.
what i want is, for example, x^2 + x, if i substitue x with 2, it should give
6.
thanks.

r*y2004-07-23 07:07

2 楼

Let me give you an example
syms x y
y = x^2 + x;
x = 2;
z = eval(y);
x = 4;
z1 = eval(y);
Now z = 6 and z1 = 20;
The trick is first to let y=f(x) when x and y are both sym var,
then redefine x to numerical values.
Or even simpler
y = 'x^2+x';
x = 2;
eval(y)
It will do it too.

【在 o*****l 的大作中提到】

: i need conversation between symbolic expression and numerical one frequently.
: tried the command: subs(S,old,new). which can just substitute one specific
: symbol.
: what i want is, for example, x^2 + x, if i substitue x with 2, it should give
: 6.
: thanks.