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## Re: Octave Error with Bounds

 From: Doug Stewart Subject: Re: Octave Error with Bounds Date: Mon, 12 Dec 2016 21:27:20 -0500

On Mon, Dec 12, 2016 at 7:12 PM, darkstyle86 wrote:
Yes, it worked!  Obviously, I need more Octave training.  Now for my second question about obtaining a curve for a single I value from my 2-D solution.  I tried "T1=T(20,j);" for the curve at I=20 and "plot(y,Texact,y,T1)" to compare the T1 curve and my Texact curve and I got the attached plot.  I know it should be a curve and not a flat line.  Any help with this one?  Thank you.

Chris W

I don't know what you want so I cannot help!

plot.pdf shows a curve!

________________________________
From: Doug Stewart-4 [via Octave] <ml-node+s1599824n4681008h46@n4.nabble.com>
Sent: Monday, December 12, 2016 6:39 PM
To: darkstyle86
Subject: Re: Octave Error with Bounds

On Mon, Dec 12, 2016 at 3:50 PM, darkstyle86 <[hidden email]</user/SendEmail.jtp?type=node&node=4681008&i=0>> wrote:
Great! That worked! Thank you.  Now that I got using a constant value to initialize temperatures out of the way, my real goal is to use a 1-D temperature solution to initialize the temperatures everywhere for the 2-D solution and plot the 1-D solution on the same graph as the 2-D solution.

1) To do the initialization, I'm using the following lines (similar lines to what I provided earlier):

"% Initialization of temperatures using 1-D analytical solution

for i=1:M
for j=1:N T(i,j)=Texact; end
end"

this is just a guess but:

Would

for i=1:M
for j=1:N T(i,j)=Texact(j); end
end"

work?

As a reminder, my y vector is defined with"for j=1:N y(j)=dy*j; end", and

my 1-D solution Texact is defined as "Texact=Tinf+(Q*(L^0.5)*besseli(0,(2*m*y.^0.5)))/(k*m*besseli(1,(2*m*L^0.5)));"

When I run the code, I'm getting the following error:

"error: Project_solver_w_areas: A(I,J,...) = X: dimensions mismatch
error: called from
Project_solver_w_areas at line 67 column 21"

Line 67 is the line "for j=1:N T(i,j)=Texact; end"

I'm sure the problem has to do with Texact only being based on a single column y vector but I don't know how to get around this.

2) When I try to plot the 2-D solution T(i,j) (using the highlighted code below), I'm getting the attached plot.  I'm assuming this is because Octave is plotting the curve (as a function of y(j)) for every value of i.  Is this as easy changing my plot function to only plot T(1,j) or whatever value of i I want?  If so, how do I do this (so that only one curve is shown)?

Thank you for your continued help, you're a lifesaver.

________________________________
From: Doug Stewart-4 [via Octave] <[hidden email]</user/SendEmail.jtp?type=node&node=4681008&i=1>>
Sent: Monday, December 12, 2016 6:50 AM
To: darkstyle86
Subject: Re: Octave Error with Bounds

On Mon, Dec 12, 2016 at 1:52 AM, darkstyle86 <[hidden email]</user/SendEmail.jtp?type=node&node=4681004&i=0>> wrote:
Good! When I add c(N)=0 to the code, the code progresses but the error changes to:

error: Project_solver_w_areas: A(I,J): row index out of bounds; value 41 out of bound 40
error: called from
Project_solver_w_areas at line 71 column 13

I think it has to do with how I'm initializing the temperatures values in T(i,j) under "Initialization of temperatures using 1-D analytical solution".  But it's a similar problem with bounds.  Any ideas here?  I tried adding a(1)=0 to the code and that didn't help.  Thank you.

________________________________
From: Doug Stewart-4 [via Octave] <[hidden email]</user/SendEmail.jtp?type=node&node=4681004&i=1>>
Sent: Friday, December 9, 2016 10:26 PM
To: darkstyle86
Subject: Re: Octave Error with Bounds

On Fri, Dec 9, 2016 at 8:24 PM, darkstyle86 <[hidden email]</user/SendEmail.jtp?type=node&node=4680990&i=0>> wrote:
Hello, there may be a post that helps me with my exact problem but I haven't
found it yet, so please direct me to that post if you know of it.  Thank
you.  I'm putting a code together to determine the 2-D temperature
distribution in a triangular fin.

My base code is as follows:

M=41; % number of grid points in x-direction
N=31; % number of grid points in y-direction
dx=w/(M-1); % delta x
dy=L/(N-1); % delta y
for i=1:M x(i)=dx*i; end
for j=1:N y(j)=dy*j; end
h=2*C*w^-0.5;

% Initialization of temperatures using 1-D analytical solution
for j=1:N
for i=2:(M-1) T(i,j)=Tinf; end

change   this
for i=2:(M-1) T(i,j)=Tinf; end
to
for i=2:(M) T(i,j)=Tinf; end

end
%
for iter=1:10
% forward sweep
for i=2:(M-1)
b(1)=-(k*dx*t/L*dy/2*dx+2*k*dy*1/8*t/L*dy^2+h*dx*dy*dx*hyp/L*dy);
c(1)=k*dx*t/L*dy/2*dx;

d(1)=-k*dy*1/8*t/L*dy^2*T(i+1,j)-k*dy*1/8*t/L*dy^2*T(i-1,j)-h*dx*dy*dx*hyp/L*dy*Tinf;
for j=2:(N-1)
a(j)=k*dx*t/L*dy*(j-1.5)*dx;

b(j)=-(k*dx*t/L*dy*(j-0.5)*dx+k*dx*t/L*dy*(j-1.5)*dx+2*k*dy*t/L*(j-1)*(dy^2)+h*dx*dy*2*dx*hyp/L*dy);
c(j)=k*dx*t/L*dy*(j-0.5)*dx;

d(j)=-k*dy*t/L*(j-1)*(dy^2)*T(i+1,j)-k*dy*t/L*(j-1)*(dy^2)*T(i-1,j)-h*dx*dy*2*dx*hyp/L*dy*Tinf;
end
a(N)=k*dx*t/L*dy*(j-1.5)*dx;

b(N)=-(k*dx*t/L*dy*(N-1.5)*dx+2*k*dy*1/2*(t+(t/L)*(L-(dy/2)))*dy/2+h*dx*dy*dx*hyp/L*dy);

d(N)=-k*dy*1/2*(t+(t/L)*(L-(dy/2)))*dy/2*T(i-1,j)-k*dy*1/2*(t+(t/L)*(L-(dy/2)))*dy/2*T(i+1,j)-Q*dx*dy*t/L*(N-1)*dy*dx-h*dx*dy*dx*hyp/L*dy*Tinf;

you should have a c(N)= something here.

Ttemp=TDMAsolver(a,b,c,d);
for j=1:N T(i,j)=Ttemp(j); end
end
end

The function TDMAsolver I am using is the following code:

function x = TDMAsolver(a,b,c,d)
%a, b, c are the column vectors for the compressed tridiagonal matrix, d is
the right vector
n = length(b); % n is the number of rows.  The first row is i=1.

% Modify the first-row coefficients
c(1) = c(1) / b(1);    % Division by zero risk.
d(1) = d(1) / b(1);    % Division by zero would imply a singular matrix.

for i = 2:n
id = 1 / (b(i) - c(i-1) * a(i));  % Division by zero risk.
c(i) = c(i)* id;                % Last value calculated is redundant.
d(i) = (d(i) - d(i-1) * a(i)) * id;
end

% Now back substitute.
x(n) = d(n);
for i = n-1:-1:1
x(i) = d(i) - c(i) * x(i + 1);
end

The error I'm getting when I run my base code is:

"error: TDMAsolver: A(I): index out of bounds; value 31 out of bound 30
error: called from
TDMAsolver at line 11 column 10
Project_solver_w_areas at line 80 column 14"

I can't figure out what the problem is.  Does anyone have any ideas?  Thank
you.

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2-D.pdf (11K) <http://octave.1599824.n4.nabble.com/attachment/4681006/0/2-D.pdf>

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