Fix error that says invalid first argument

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Aparajita
Aparajita 2023-11-23
编辑： Dyuman Joshi 2023-11-29
syms x y L
f = input('Enter the function f(x,y): '); % f(x,y)= x*y ; x^2+y^2
g = input('Enter the constraint function g(x,y): '); % g(x,y)= ((x^2)/8)+((y^2)/2)-1 ; x+y-10
F = f + L*g;
gradF = jacobian(F,[x,y]);
[L,x1,y1] = solve(g,gradF(1),gradF(2),'Real',true); % Solving only for Real x and y
x1 = double(x1); y1 = double(y1);
xmx = max(x1); xmn = min(x1); % Finding max and min of x-coordinates for plot range
ymx = max(y1); ymn = min(y1); % Finding max and min of y-coordinates for plot range
range = [xmn-3 xmx+3 ymn-3 ymx+3]; % Setting plot range
ezmesh(f,range);hold on; grid on;
h = ezplot(g,range); set(h,'LineWidth',2);
tmp = get(h,'contourMatrix');
xdt = tmp(1,2:end); % Avoiding first x-data point
ydt = tmp(2,2:end); % Avoiding first y-data point
zdt = double(subs(f,{x,y},{xdt,ydt}));
plot3(xdt,ydt,zdt,'-o','Color','b','MarkerSize',10);axis(range);
for i = 1:numel(x1)
G(i) = subs(f,[x,y],[x1(i),y1(i)])
plot3(x1(i),y1(i),G(i),'*k','MarkerSize',20);
end
title('Constrained Maxima/Minima')
  2 个评论
Dyuman Joshi
Dyuman Joshi 2023-11-23
编辑：Dyuman Joshi 2023-11-29
What do you expect this line of code to do? What is the idea behind it?
[L,x1,y1] = solve(g,gradF(1),gradF(2),'Real',true); % Solving only for Real x and y
Edit - ezplot is not recommended to use. Use fplot instead.
Walter Roberson
Walter Roberson 2023-11-29
The "plot range" had to be moved to the end of the previous lines

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回答（1 个）

Rangesh
Rangesh 2023-11-29
Hi Aparjita,
I understand that you want to address the issue of an invalid first argument.
The error is occurring because the plot range is not in a valid syntax. If you comment out that section of the code, it should work fine. It seems like you are attempting to limit the axis of the plot. To achieve this, you can refer to the documentation on how to properly set the plot range:
https://in.mathworks.com/help/matlab/ref/axis.html
I hope this resolves your query.
Thanks,
Rangesh.

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