Wrong loop, please help!

Question

surawut.A 2021-12-19

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1614165-wrong-loop-please-help

评论： Image Analyst 2021-12-19

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

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

Please help & thank you for any help.

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Answer 1

Image Analyst 2021-12-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1614165-wrong-loop-please-help#answer_858350

在 MATLAB Online 中打开

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.

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Image Analyst 2021-12-19

在 MATLAB Online 中打开

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 2021-12-19

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

this one it x y z.

Image Analyst 2021-12-19

scatteredInterpolant_Demo.m

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?

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