Help with a two variables equation?

Hi there, Im trying to create a 3D graph of the Constant Surface Heat flux in a material. The equation is in the pic i added. The thing is, i get problems with multiplying the matrices (x and t).. What am i doing wrong? is there any one who can help write this code? Thank you! (the only variables are x and t, all others are constant.)

[Star Strider]

Posting your code would help significantly.

We’re good, but we can’t guess what code you’ve written.

[Nir]

This is my code and what i get is in the picture

clc; clear variables; close all;

x=0:0.01:10;
t=0:0.01:10;
alpha=11.23*10^-5;
Ti=20;
k=368;
q=0.5*10^6;

T(x,t)=((2*q)/(k))*sqrt((alpha*t)/pi).*exp((-(x.^2))/4*alpha*t')-((q*x)/(k)).*(1-erf(x/(sqrt(2*alpha*t))))-Ti;

Answer 1

[Roger Stafford]

In the line

   T(x,t)=((2*q)/(k))*......

if T is to be a matrix of values, then the 'x' and 't' values must be indices which are positive integers, and that is not the case with your code. For generating a surface in 3D you should use 'meshgrid' or 'ndgrid' to create a grid of value pairs and then call on 'surf'.

   [x,t] = meshgrid(0:0.01:10,0:0.01:10);
   T = ((2*q)/(k))*......
   surf(x,y,T)

Also I notice several discrepancies between the image of "T(x,t) = ..." equation and the equation you have coded:

1) The -Ti on the left should become +Ti on the right.

2) exp((-(x.^2))/4*alpha*t') should be exp(-x.^2./(4*alpha*t)).

3) x/(sqrt(2*alpha*t)) should be x./(2*sqrt(alpha*t)).

Also it was not necessary to convert the erfc to 1-erf, since matlab already has an erfc function.

[Nir]

I tried that but still the code just wont work.. this is my code now:

clc;
clear variables;
close all;

x=0:0.01:10; t=0:0.01:10; alpha=11.23*10^-5; Ti=20; k=368; q=0.5*10^6;

T(x,t)=((2*q)/(k))*sqrt((alpha*t)/pi).*exp(-x.^2/4*alpha*t)-((q*x)/(k)).*(erfc(x./(2*sqrt(alpha*t))))+Ti;

Thank you so much for the help!

[Roger Stafford]

You didn't take my and Mohammad Abouali's advice on 2):

2) exp((-(x.^2))/4*alpha*t') should be exp(-x.^2./(4*alpha*t)).

Without that added 'dot' it would give you the error message. Also you are multiplying by alpha*t here and the operation shown in your original image requires that you divide by these quantities.