Wrong loop, please help!

clear all
clc
%%input parameter%%
R=8.314;
T=[873:100:1073];%%%K
Cs=[15 30 45];%%Carbon at surface
Cx=0.12;
C0= 0.08;%Carbon in specimen 
t=3600;% sec
% find diffusion coefficients
D=-0.27*(1.04/-0.22)*exp((-246)./(R*T));%(unit: cm^2*sec^-1)
% use D to find how far that carbon can diffusion
Erf = (Cs-Cx)./(Cs-C0);
z=NaN(size(Erf));
for n=1:numel(Erf)
    if Erf(n)<2
        z(n)=(-0.3725*Erf(n)^2)+(1.2144*(Erf(n)))+(0.0006);%error(0.01-0.08%)  0.4286
    else
        z(n)=(-0.0109*Erf(n)^2)+(0.0577*(Erf(n)))+(0.9235);%error(<0.01%)
    end
    %find X6
    x=z*(2*sqrt(D*t));%%% ***t=3600 ประกาศตัวแปลเพิ่ม หน่วย***
end

%Graph 1
T=[873:100:1073];
Cs=[0.15 0.30 0.45];
[T,Cs]=meshgrid(T,Cs);
x=z(n)*(2*sqrt(D*t));
mesh(T,Cs,x)
Ylabel('length Carbon can diffuse(cm)','fontsize',18);
Xlabel('temperature (°C)','fontsize',18);
Zslabel('CarbonStart ,fontsize',18);

If you run program, the problem on Z. After looping I got 3 Z and all correct but on x formula, I cant use Z. I try use z(n) but it like average from looping. X should have 9 answer isnt it? also cant continue plot 3d graph because Z must be matrix.

So I have 2 problem

1. I can't use z from loop
2. I can't plot 3d graph

Please help & thank you for any help.

Answer 1

[Image Analyst]

You assign x inside the loop and outside. You can just do it in one place. If you want to assign it inside, you have

x=z*(2*sqrt(D*t));

when you should probably have

x(n) = z(n) * (2*sqrt(D*t));

If you want to do it outside the loop instead, you should probably do

x = z * (2*sqrt(D*t));

but again, you don't need to assign x in both places.

[surawut.A]

thank you for your help, but i try to use your code and it says

Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

Error in MatlabNEWWWWW (line 22)

x(n) = z(n) * (2*sqrt(D*t));

[Image Analyst]

OK, this fixes the x and z stuff but I don't know what you're wanting to plot or do with mesh():

%%input parameter%%
R=8.314;
T=[873:100:1073];%%%K
Cs=[15 30 45];%%Carbon at surface
Cx=0.12;
C0= 0.08;%Carbon in specimen
t=3600;% sec
% find diffusion coefficients
D=-0.27*(1.04/-0.22)*exp((-246)./(R*T))  %(unit: cm^2*sec^-1)

D = 1×3

1.2338 1.2381 1.2416

% use D to find how far that carbon can diffusion
Erf = (Cs-Cx)./(Cs-C0);
z=NaN(size(Erf));
scalingFactor = 2*sqrt(D*t)

scalingFactor = 1×3

133.2934 133.5258 133.7151

for n = 1 : numel(Erf)
    if Erf(n)<2
        z(n)=(-0.3725*Erf(n)^2)+(1.2144*(Erf(n)))+(0.0006);%error(0.01-0.08%)  0.4286
    else
        z(n)=(-0.0109*Erf(n)^2)+(0.0577*(Erf(n)))+(0.9235);%error(<0.01%)
    end
    %find X6
    x = z .* scalingFactor    %%% ***t=3600 ประกาศตัวแปลเพิ่ม หน่วย***
end

x = 1×3

112.1316 NaN NaN

x = 1×3

112.1316 112.4116 NaN

x = 1×3

112.1316 112.4116 112.5990

%Graph 1
T=[873:100:1073];
Cs=[0.15 0.30 0.45];
[T,Cs]=meshgrid(T,Cs);
x = z .* scalingFactor; % Not needed here since it was computed inside the loop.
mesh(T,Cs,x)

Error using mesh (line 71)
Z must be a matrix, not a scalar or vector.

Ylabel('length Carbon can diffuse(cm)','fontsize',18);
Xlabel('temperature (°C)','fontsize',18);
Zslabel('CarbonStart ,fontsize',18);

[surawut.A]

thank you very much

if not bothering you,

as you can see at

Erf = (Cs-Cx)./(Cs-C0);

z=NaN(size(Erf));

scalingFactor = 2*sqrt(D*t)

z=Erf so it have 3 answer

and also scalingFactor use D from above, have 3 answer same

so it should have 9 answer or am i wrong

but anyway big thank to you

[Image Analyst]

So do you want a 3x3 matrix where we have a value for each of the 3 z values combined with each of the 3 D values? And what is x for?

[surawut.A]

I want to plot 3d graph by using

x=length Carbon can diffuse

T=Temperature

Cs=CarbonStart

the value of z and D use to find x

Im really new to this :(

[Image Analyst]

So do you want a bar chart where x and y are two of those things, and the bar height is another of those things?

Tell me which chart here:

https://www.mathworks.com/products/matlab/plot-gallery.html

is closest to what you want/expect to see.

[surawut.A]

https://www.mathworks.com/matlabcentral/fileexchange/35305-matlab-plot-gallery-surface-plot-1

this one it x y z.

[Image Analyst]

OK, use surf(). So x is x, ,y is Cs, and z (surface height) is T?

So do you have a T for every single combination of x and y? Or are some missing you you need to interpolate with scatteredInterpolant, like the attached demo?