# Find gradient ascent for 3D surface

4 views (last 30 days)
Sarah D on 28 Nov 2021
Commented: Star Strider on 29 Nov 2021
• I have a 3D surface (x,y,z) plotted using the following code (excel sheet attached):
clear; clc; clearvars;
rows = (T.(3)== 3);
T = T(rows, :);
% Define Variables
x = T.(1);
y = T.(2);
z = T.(4);
xi = linspace(min(x),max(x), 200);
yi = linspace(min(y),max(y), 200);
[X,Y] = meshgrid(xi,yi);
Z = griddata(x,y,z,X,Y);
surf(X,Y,Z);
• The generated surface looks as follows:
• I am trying to plot a line that incrementally goes from the starting point (0,0,14.19) to the highest point on the surface.
• I have seen other answers on the forums dealing with analytical functions. However, in here, I only have the surface generated from points. Hence, how could I be able to do it from these points?

Star Strider on 28 Nov 2021
This code finds the maximum of the surface and then uses griddedInterpolant with the calculated ‘xv’ and ‘yv’ vectors to draw the interpolated line, following the ‘Z’ contours.
T = 161599×6 table
in:xrot in:yrot in:n out:PE out:ARM out:r _______ _______ ____ ______ _______ _____ 0 0 3 14.19 0 0.63 0.01 0 3 14.19 0.33 0.63 0.02 0 3 14.19 0.67 0.63 0.03 0 3 14.2 1 0.63 0.04 0 3 14.21 1.33 0.63 0.05 0 3 14.22 1.67 0.63 0.06 0 3 14.24 2 0.63 0.07 0 3 14.25 2.33 0.63 0.08 0 3 14.27 2.67 0.63 0.09 0 3 14.29 3 0.63 0.1 0 3 14.32 3.34 0.63 0.11 0 3 14.35 3.65 0.63 0.12 0 3 14.38 3.95 0.63 0.13 0 3 14.41 4.21 0.63 0.14 0 3 14.44 4.46 0.63 0.15 0 3 14.48 4.68 0.63
rows = (T.(3)== 3);
T = T(rows, :);
% Define Variables
x = T.(1);
y = T.(2);
z = T.(4);
xi = linspace(min(x),max(x), 200);
yi = linspace(min(y),max(y), 200);
[X,Y] = ndgrid(xi,yi);
Z = griddata(x,y,z,X,Y);
zmix = find(Z == max(Z(:))) % There Is More Than One Maximum
zmix = 4×1
17202 17402 18005 18204
Xc = X(zmix);
Yc = Y(zmix);
Zc = Z(zmix);
Xcm = mean(Xc);
Ycm = mean(Yc);
Zcm = mean(Zc);
xv = linspace(0, Xcm, 100);
yv = linspace(0, Ycm, 100);
Zi = griddedInterpolant(X,Y,Z);
zv = Zi(xv,yv);
figure
surf(X,Y,Z, 'EdgeColor','none', 'FaceAlpha',0.5);
hold on
stem3(Xcm,Ycm,Zcm,'-^r', 'filled')
plot3(xv, yv, zv, '-m', 'LineWidth',2)
hold off
colormap(turbo)
xlabel('X')
ylabel('Y')
zlabel('Z')
title('Original: Complete Surface & Requested Line')
figure
surf(X,Y,Z, 'EdgeColor','none', 'FaceAlpha',0.5);
hold on
stem3(Xcm,Ycm,Zcm,'-^r', 'filled')
plot3(xv, yv, zv, '-m', 'LineWidth',2)
hold off
colormap(turbo)
xlabel('X')
ylabel('Y')
zlabel('Z')
xlim([0 2*Xcm])
ylim([0 2*Ycm])
zlim([10 20])
view(290,30)
title('Detail: Zoomed Surface Section & Requested Line')
Choose different lime colours & colormap options to get the desired result.
.
##### 2 CommentsShowHide 1 older comment
Star Strider on 29 Nov 2021
As always, my pleasure!
.

Alan Weiss on 28 Nov 2021
You might be interested in this example: Pattern Search Climbs Mount Washington
Alan Weiss
MATLAB mathematical toolbox documentation

R2021b

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