Problem plotting a 3-D function

Hi there

I need to plot 2 3-D functions an see how they intersect. However I am experiencing problems with one of the functions (z1). Apparently i am calculating it wrong, therefor my input for z1 is wrong. Can somebody help me? This should be rather easy for someone with experience ;)

This is the code:

% Define the input grid
clc, clear, close all
[x, y] = meshgrid(linspace(0,400,40),linspace(0,30000,40));
grid on
xlabel('Stress [MPa]')
ylabel('Time [h]')
zlabel('Creep Strain [-]')

% Calculate the two surfaces
A1 = -8.269000000000000;
m1 = 2.071000000000000;
m2 = 0.239700000000000;
B1 = -13.100000000000000;
n1 = 2.813000000000000;
B2 = -49.960000000000001;
n2 = 18.170000000000002;
z1 = 10^A1*x.^m1*y.^m2+y.*(10^B1*x.^n1+10^B2*x.^n2);
z2 = 0*x+0*y+0.01;

% Visualize the two surfaces
surface(x, y, z1, 'FaceColor', [0.5 1.0 0.5], 'EdgeColor', 'none');
surface(x, y, z2, 'FaceColor', [1.0 0.5 0.0], 'EdgeColor', 'none');
view(3); camlight; axis vis3d

Answer 1

[David Sanchez]

try to hold on the current figure and change your point of view:

% Define the input grid clc, clear, close all 
[x, y] = meshgrid(linspace(0,400,40),linspace(0,30000,40)); 
grid on 
xlabel('Stress [MPa]') 
ylabel('Time [h]') 
zlabel('Creep Strain [-]')
% Calculate the two surfaces 
A1 = -8.269000000000000; 
m1 = 2.071000000000000; 
m2 = 0.239700000000000; 
B1 = -13.100000000000000; 
n1 = 2.813000000000000; 
B2 = -49.960000000000001; 
n2 = 18.170000000000002; 
z1 = 10^A1*x.^m1*y.^m2+y.*(10^B1*x.^n1+10^B2*x.^n2);
z2 = 0*x+0*y+0.01;
% Visualize the two surfaces 
surface(x, y, z1, 'FaceColor', [0.5 1.0 0.5], 'EdgeColor', 'none'); hold on
surface(x, y, z2, 'FaceColor', [1.0 0.5 0.0], 'EdgeColor', 'none'); hold off
view([30,30]); 
camlight; 
axis vis3d

[Ben]

It is not a question of the view ;) Somehow I am calculating the function z1 wrong! I think it is because of my input of the values x and y as a grid and how I apply them in the function z1. Probably i am using elementwise multiplication wrong, bu I do not know how to solve this problem!

[David Sanchez]

Is your z1 function this one?

z1 = (10^A1).*(x.^m1).*(y.^m2)  + y.*( (10^B1).*(x.^n1) + (10^B2).*(x.^n2) );

Since we don't know your function, there is no way to help you further. Could you be more specific?

[Ben]

yes that is the function z1! if you for example enter x = 1 and y = 1 you will get other results for z1(1,1) then i you use meshgrid and linspace to define x and y

Answer 2

[David Sanchez]

Well, I think you are having a scale issue. Your z1 is right, and the way to plot your data as well is right, but bear in mind the scale of your result ( z1 ). You are plotting an exponential function, and as such, there will be a big difference in the results you obtain with an insignificant change of your input values. I figure out you know that your z2 is just a plane on z=0.01. Make sure your z1 is exactly what you want.

[Ben]

I know what you are thinking, but have a look at this. If i enter

input: x = 1; y = 1; z1 = 10^A1*x.^m1*y.^m2+y.*(10^B1*x.^n1+10^B2*x.^n2);

output: z1 = 5.382777257986354e-009

However if I enter

Input: [x, y] = meshgrid(linspace(0,400,400),linspace(0,10,400)); z1 = 10^A1*x.^m1*y.^m2+y.*(10^B1*x.^n1+10^B2*x.^n2); smallestvalue = min(min(z1));

output: smallestvalue = 1.887491724543205

So you can see there is definitely an error while calculating the function z1, I just do not know what I am doing wrong

[Iain]

Its a case of garbage in, garbage out.

Check that your x and y values output by meshgrid include (1,1). I suspect you'll need to change it to linspace(0,400,401) and linspace(0,10,401)