Find the minimum of a multi-variable function

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emonhossain roy
emonhossain roy 2019-6-23
编辑： infinity 2019-6-23
Question: Find the minimum of in the window [0,2]×[2,4] with increment 0.01 for x and y.
My approach:
syms fun(x,y) fx(x,y) fy(x,y) fxy(x,y) x y
=;
;
;
;
pt=solve([==0,==0],[x y]) But it gives me an error.
besides what about the window and increment mentioned that question. Any solution will be appreciated .
Thanks in advance .
  2 个评论
infinity
infinity 2019-6-23
Hello,
Could you provide your code and show us what is the error?
emonhossain roy
emonhossain roy 2019-6-23
code:
clc
clear all
syms fun(x,y) fx(x,y) fy(x,y) fxy(x,y) x y
fun(x,y)=x^2+y^2-2*x-6*y+14;
fx(x,y)=diff(fun(x,y),x);
fy(x,y)=diff(fun(x,y),y);
fxy(x,y)=diff(fx(x,y),y);
pt=solve([fx(x,y)==0,fy(x,y)==0],[x y])
error:
Warning: 4 equations in 2 variables.
> In C:\Program Files\MATLAB\R2013a\toolbox\symbolic\symbolic\symengine.p>symengine at 56
In mupadengine.mupadengine>mupadengine.evalin at 97
In mupadengine.mupadengine>mupadengine.feval at 150
In solve at 170
Warning: Explicit solution could not be found.
> In solve at 179
pt =
[ empty sym ]

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infinity
infinity 2019-6-23
编辑：infinity 2019-6-23
Hello,
In your code, it was not good to put the name like "fun(x,y)". Also, we do not need to declare "fx, fun, fy,.." as symbolic variable. Here is a small code that you can refer
clear
syms x y
fun=x^2+y^2-2*x-6*y+14;
fx=diff(fun,x);
fy=diff(fun,y);
pt=solve([fx==0,fy==0],[x y]);
% pt=solve(fx==0,fy==0);
sol = struct2array(pt)
It will give us the solution
sol =
[ 1, 3]
I have run this code on Matlab2018a. Maybe in your Matlab version, there will be some different.

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