how to replace variable by another variable

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vikas singh 2023-2-8

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评论： vikas singh 2023-4-29

Hn=-2*P/(Mu*exp(n^2*pi^2*T/Mu))

I want to replace T by t and want to do calculation

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Venkat Siddarth 2023-2-8

Hi @vikas singh,

Can you elaborate the query,on whats the result you are getting when you replace "T" with "t" in the equation itself i.e

Hn=-2*P/(Mu*exp(n^2*pi^2*t/Mu))?

vikas singh 2023-2-10

actually I have to replace T by t/L and again i have to give different value to t for calculation. and some for loop is also involve in the equation for n

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回答（3 个）

Walter Roberson 2023-2-8

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https://ww2.mathworks.cn/matlabcentral/answers/1908690-how-to-replace-variable-by-another-variable#answer_1166450

if you are using the symbolic toolbox then subs()

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vikas singh 2023-2-13

can you please tell me if I want to give value of t as 5, 10, 15, 20,25,.......,1000 then how to give here in the code. thanks in advance.

Walter Roberson 2023-2-13

在 MATLAB Online 中打开

subs(Hn_new, t, (5:5:1000).')

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vikas singh 2023-2-15

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https://ww2.mathworks.cn/matlabcentral/answers/1908690-how-to-replace-variable-by-another-variable#answer_1171845

when I'm using the following code to evaluate z value . I'm getting the Q value and all the value after Q is zero. I m not getting where I'm wrong.

clc;

clear all;

close all;

l=10000;

x=0:100:l;

t=[0;1;5;10;15;20;25];

H=30;

Mu=2.8e-1;

D=31;

k=0.01132;

k1=l/H;

for n=1:100

a=2*H;

b=(1-(-1)^n*exp(-k*l))/((n*pi+(k^2*l^2)/(n*pi)));

c=1/(n*pi);

Cn(n)=a*(b-c);

end

s=0;

for n=1:100

d= sin(n*pi*x/l);

q= exp((-n^2*pi^2*t)/(Mu^2*l));

aa=Cn(n).*d.*q;

s=s+aa;

end

syms X T

for n=1:100

H0=@(X,T)Cn(n).*sin(n*pi*X).*exp(-n^2*pi^2*T/Mu)+H*X/(D-H)+H/(D-H);

y=diff(H0*diff(H0,X),X);

Q=int(y*sin(n*pi*X),X,0,1);

P=int(Q*exp(n^2*pi^2*T/Mu),T,0,T);

Hn=-2*P/(Mu*exp(n^2*pi^2*T/Mu));

H1=Hn.*sin(n*pi*X);

for i=1:size(t,1)

for j=1:length(x)

H=(subs(H1,{X,T},{x(j)/l,t(i,1)/(Mu*l)}));

ZZ(j,1)=double(H);

end

XX(i,1)=sum(ZZ);

clear ZZ

end

s1=((D-H)^2).*XX/l;

end

j=(H*x)/l;

z=s-j-s1

plot(x,z)

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vikas singh 2023-4-25

I want to multiply r and f value in the following code. how to do it.

clc;

clear all;

close all;

L=600;

T=365;

delt=0.025;

k=8.64;

aa=delt*k*(1+delt);

epc=0.3;

H=50;

mu=epc/(k*delt*H);

w1=86400*1*10^-8;

w2=8*86400*10^-8;

dx=1;

dt=1;

d=(mu*dt)/(dx^2);

N=L/dx +1;

M=T/dt +1;

for i=1:N

x(i)=0+(i-1)*dx;

end

for n=1:M

t(n)=0+(n-1)*dt;

end

for n=1:M

for i=1:N

if x(i)>=250 && x(i)<=350

r(i)=w2;

else

r(i)=w1;

end

if t(n)<=182.5

f(n)=sin(2*pi*t(n)/365).^2;

else

f(n)=0;

end

Walter Roberson 2023-4-25

在 MATLAB Online 中打开

r.*f

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vikas singh 2023-4-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1908690-how-to-replace-variable-by-another-variable#answer_1222614

编辑：Walter Roberson 2023-4-25

在 MATLAB Online 中打开

I'm writing the following but it is giving me zero and showing matrix dimension is not agree

clc;
clear all; 
close all;
L=600;
T=365;
delt=0.025;
k=8.64;
aa=delt*k*(1+delt);
epc=0.3;
H=50;
mu=epc/(k*delt*H);
w1=86400*1*10^-8;
w2=8*86400*10^-8;
dx=1;   
dt=1;
d=(mu*dt)/(dx^2);
N=L/dx +1;  
M=T/dt +1; 
for i=1:N 
    x(i)=0+(i-1)*dx;
end
for n=1:M
    t(n)=0+(n-1)*dt;
end
for n=1:M 
    for i=1:N
        if x(i)>=250 && x(i)<=350
            r(i)=w2;
        else
            r(i)=w1;
        end
        
    end
    if t(n)<=182.5
        f(n)=sin(2*pi*t(n)/365).^2;
    else
        f(n)=0;
    end 
    f2=r.*f
end 
f2 = 1×601
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
Arrays have incompatible sizes for this operation.

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Walter Roberson 2023-4-28

I want to plot between x and -(z(n+1,i)).^0.5

Do you mean that you have an independent variable 1:N on the x axis, and you want to treat the variable x and that particular expression as dependent variables to be drawn and you want to fill the area between the two lines?

Or is your x variable to be treated as the x axis and you want to draw -(z(n+1,i)).^0.5 even though that appears to be independent of x?

vikas singh 2023-4-29