Why is matlab not evaluating equation correctly

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Josh McCaffrey
Josh McCaffrey 2015-3-28
评论： Star Strider 2015-3-28
x1=sym('x1');
x2=sym('x2');
a=sym('a');
fx0(x1,x2) = 10*((x1)+3)^2+(x2)^2;
sp=[-1 , 1];
fx0d(x1,x2) = gradient(fx0);
dsd = -1*fx0d(sp(1,1),sp(1,2));
dsd1 = fx0(sp(1,1)+a*dsd(1,1),sp(1,2)+a*dsd(2,1))
When I run this code the variable dsd1 is not correct. The correct answer is 10(-40a+2)^2+(1-2a)^2 but matlab returns (2*a - 1)^2 + 10*(40*a - 2)^2 and I have no idea why.

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Star Strider
Star Strider 2015-3-28
When I use your code, and then also add at the end of that code:
Q = 10*(-40*a+2)^2+(1-2*a)^2;
Q = simplify(Q, 'steps', 10)
and run it, I get as the result:
dsd1 =
(2*a - 1)^2 + 10*(40*a - 2)^2
Q =
(2*a - 1)^2 + 10*(40*a - 2)^2
Unless I’m missing something, those look a lot alike!

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