How to Substitute an array into an equation and solve it ?

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Kalpha.mc
Kalpha.mc 2020-11-15
编辑： Ameer Hamza 2020-11-16
So if i had a = [1 2 3] b = [4 5 6] c = [7 8 9]
and the equation is ax^2+bx+c = 0
How would i substitude the array and solve for x ?

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回答（1 个）

Ameer Hamza
Ameer Hamza 2020-11-15
编辑：Ameer Hamza 2020-11-15
For the given value of a, b, and c, the equation have no real solutions. Following shows how to use fsolve() when the equations have solutions
a = [1 2 3];
b = [4 5 6];
c = [-7 -8 -9];
F = @(x) a(:).*x.^2+b(:).*x+c(:);
sol = fsolve(F, rand(3,1))
If you don't have optimization toolbox, then you can use fzero()
a = [1 2 3];
b = [4 5 6];
c = [-7 -8 -9];
sol = zeros(size(a));
for i=1:numel(a)
F = @(x) a(i).*x.^2+b(i).*x+c(i);
sol(i) = fzero(F, rand());
end
  2 个评论
Ameer Hamza
Ameer Hamza 2020-11-15
No, you are not using subs() correct. Following shows how it needs to be done
syms x a b c
C = a * (x.^2) + (b * x) + c == 0;
x1 = subs(C,{a,b,c},{1,3,5});
solution = double(solve(x1,x));
Ameer Hamza
Ameer Hamza 2020-11-16
编辑：Ameer Hamza 2020-11-16
If a, b, and c are arrays
syms x a b c
av = [1 2 3];
bv = [4 5 6];
cv = [7 8 9];
C = a * (x.^2) + (b * x) + c == 0;
solution = cell(size(av));
for i = 1:numel(av)
x1 = subs(C,{a,b,c},{av(i),bv(i),cv(i)});
solution{i} = double(solve(x1,x));
end
solution is a cell array, where each cell contain solution for a combination of a, b, and c.

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