Question

求问matlab大神如何求解参数方程的参数值

举个简单的例子，y=a*x^2+b*x
已知y(2)-y(1)=0
y(3)+y(4)=5
求出a，b的值。

syms a b x y f1 f2;
y=a*x^2+b*x;
f1=subs(y,x,1)-subs(y,x,0);
f2=subs(y,x,3)+subs(y,x,4);
[a,b]=solve('f1=0','f2=5','a','b')

这样做为什么不行啊，大神应该怎么写啊。

Answer 1

Hi, I have tested your code. It seems you have almost done most of work but neglect a tiny error inside.

Also I would like to mention that the incorrect documentation 2014a may be a trick for you to successfully debug your error.

For example:

syms u v
[sv,su] = solve([2*u^2+v^2 == 0, u-v == 1], [v,u]) % Doesn't work

Just be wary of it. Here is my solution for solvin multivariate equations followed by:

clear all

syms a b x y f1 f2;

y = a*x^2+b*x;

f1 = subs(y,x,2)-subs(y,x,1);
f2 = subs(y,x,3)+subs(y,x,4);

[sa,sb] = solve([f1 == 0, f2 == 5], a, b);

fprintf('a = %s\n',char(sa))
fprintf('b = %s\n',char(sb))

The output should be

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