MATLAB: Find a max value in function

function max value

[x,y] = meshgrid(-2 : 0.5 : 2 , -5 : 0.5 : 5);
z = ( 5*x.^2 )+( y.^3 )+10*x;
mesh(x,y,z);
xlabel('x-axis');
ylabel('y-axis');
zlabel('z-axis');

i'm troble in this problem

i ask something this problem, present i make a 3dimension function graph

and i want find a max value , min value in z and add mark to max value , min value

please help me

i'm not good at englinsh. sorry

Best Answer

Add the below after mesh() call:

mx = z==max(z(:));
mn = z==min(z(:));
hold on
plot3(x(mx),y(mx),z(mx),'ok')
plot3(x(mn),y(mn),z(mn),'or')

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MATLAB: How to find max and min of fuction of 2 independent variables

You could use a similar formulation as found here.

What it boils down to is using imregionalmax on your Z matrix to find the local maximums.

MaxVals = find(imregionalmax(Z));
plot3(X(MaxVals),Y(MaxVals),Z(MaxVals),'ro','MarkerSize',30)

Now this will find you your local maximums but to find the minimums you could just flip Z upside down and then run imregionalmax again.

Zupsidedown=-Z;
MinVals = find(imregionalmax(Zupsidedown));
plot3(X(MinVals),Y(MinVals),Z(MinVals),'go','MarkerSize',30)

This will allow you to find the local max and mins across the entire surface.

clear;clc;close all
korak=.1;
intervalpox=10;
intervalpoy=10;
x=korak:korak:intervalpox;
y=korak:korak:intervalpoy;
[X,Y] = meshgrid(x,y);
Z = (sin(sqrt(X.^2 + Y.^2)) ./ (sqrt(X.^2 + Y.^2)));
Zupsidedown=-Z;
MaxVals = find(imregionalmax(Z));
MinVals = find(imregionalmax(Zupsidedown));
plot3(X(MaxVals),Y(MaxVals),Z(MaxVals),'r.','MarkerSize',30)
hold on
plot3(X(MinVals),Y(MinVals),Z(MinVals),'g.','MarkerSize',30)
mesh(X,Y,Z)
grid on
xlabel('.x.')
ylabel('.y.')
zlabel('.z.')
title('mesh')

MATLAB: Insert 3D array into Another 3D Array

yMax - yMin

will always be 1 smaller than

yMin:yMax

because of the inclusive end points (assuming integers, of course, which we are here since they are indices).

e.g.

10 - 1 = 9

but

1:10

clearly gives an array of length 10.

You probably just need to put some +1's in your X, Y and Z

Best Answer

Related Solutions

MATLAB: How to find max and min of fuction of 2 independent variables

MATLAB: Insert 3D array into Another 3D Array

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