error?

A = [ 0 0 0.43; 0.6 0 0; 0 0.75 0.96 ];

T = [ 1 2 3 4 5 10 20 25 50 75 ];

V0 = [ 42, 0, 95 ]';

V=zeros(3,length(T));

V(:,1)=V0;

i=0;

for t=T

      i=i+1;

      V(:,1)=(A^t)*V0;

end

figure

T=[0 1 2 3 4 5 10 20 25 50 75];

T2=log(T);

V2=log(V);

LINE 22 plot( T2, V2(1,:), 'b', T2, V2(2,:), 'g', T2, V2(3,:), 'r')

%legend('calves','yearlings','adults')

title('population versus time')

xlabel('time')

LINE 30 ylabel('population')

THAT ERROR WENT AWAY. NOW IT SAYS....

??? Error using ==> plot Vectors must be the same lengths.

Error in ==> project3 at 22 plot( T2, V2(1,:), 'b', T2, V2(2,:), 'g', T2, V2(3,:), 'r')

[Image Analyst]

Try this:

V0 = [ 42; 0; 95 ]

V=zeros(3,length(T)+1);

V(:,1)=V0;

col = 1;

for t=T

col = col+1;

V(:, col)=(A.^t)*V0;

end

Answer 1

[Walter Roberson]

Which is line 48? Please show the traceback.

Image Analyst has proposed (A.^t)*V0 but I think you do want (A^t)*V0 . An array raised to a power is appropriate for a stocastic process. However, when you raise a 3 x 3 matrix to a power, you get out a 3 x 3 matrix. You then try to multiply that by a 1 x 3 matrix, which is going to be an error. I think your definition of V0 should not have the transpose at the end, and should just be

V0 = [ 42; 0; 95 ];

[Image Analyst]

They give the same thing. When I actually tried the code I found the problem was "V(:, col)=(A.^t)*V0; " as given in my comment above, and I also discovered the transpose error.

[Haley]

there isnt a line 48.

and the V0 is given in the problem as 42, 0, 95

[Walter Roberson]

The error message you posted was

??? Error using ==> project at 48

Valid object handles must be supplied

So MATLAB thinks there is a line 48. If you were to post the traceback we could try to debug -that- problem.

You are right, V0 is given in the code as [42, 0, 95] . That makes it a 1 x 3 matrix, and that matrix is appearing on the right hand side of a matrix multiply in which the left hand side is 3 x 3 . You cannot matrix-multiply a 3 x 3 matrix by a 1 x 3 matrix: in order to be able to do a matrix multiply, the second dimension (i.e., 3) of the first matrix must be the same as the first dimension of the second matrix (i.e, 1). Now, if you were to do a matrix multiply with the transpose of V0, then that would be (3 x 3) * (3 x 1) and that would be mathematically fine, producing a 3 x 1 answer.

[Haley]

it stops at line 31

[Haley]

i have a new error now

[Walter Roberson]

You only posted 19 lines of code up to and including the ylabel() line. Which line is line 31? Please post the complete traceback showing the error message and showing MATLAB's idea of the line it is having problems with.

Have you tried commanding

dbstop if error

at the command line, letting it run, and examining all of the variables on the line it stops at?

[Haley]

It stops at line 22. I put where line 22 is.

[Haley]

??? Error using ==> plot Vectors must be the same lengths.

Error in ==> project3 at 22 plot( T2, V2(1,:), 'b', T2, V2(2,:), 'g', T2, V2(3,:), 'r')

[Haley]

okay so i i edited it again and it looks like this:

A = [ 0 0 0.43; 0.6 0 0; 0 0.75 0.96 ];

T = [ 1 2 3 4 5 10 20 25 50 75 ];

V0 = [ 42, 0, 95 ]';

V=zeros(3,length(T));

V(:,1)=V0;

i=0;

for t=T

i=i+1;

V(:,1)=(A^t)*V0;

end

figure

T=[0 1 2 3 4 5 10 20 25 50 75];

%legend('calves','yearlings','adults')

title('population versus time')

xlabel('time')

ylabel('population')

.

the problem is the graph is blank

[Walter Roberson]

Replace

V(:,1)=(A^t)*V0;

with

V(:,i)=(A^t)*V0;

and, of course, restore your plot() command.

Answer 2

[Image Analyst]

Well I think

figure T=[0 1 2 3 4 5 10 20 25 50 75];

evaluates to

figure 0 1 2 3 4 5 10 20 25 50 75;

and you don't have figures with those ID numbers. Try putting a semicolon after figure or splitting that line into two lines.

[Haley]

what does that mean?

[Haley]

I put the semicolon and it didn't work

[Image Analyst]

OK, I see you now edited it so that figure is on a separate line but I don't get the error you did. When I run your code it says

??? Error using ==> mtimes

Inner matrix dimensions must agree.

Error in ==> test at 11

V(:,1)=(A^t)*V0;

Did you perhaps mean A .^ t to do an element-by-element raising to a power?

[Haley]

I got the same error as you this time but it still is not working

Answer 3

[Haley]

I figured it out. Thanks so much y'all!

[Image Analyst]

Yes, the debugger can be a more powerful tool than "Answers." Glad you learned how to use it.

[Michael Roberts]

please help; how did you figure it out?

[Michael Roberts]

my plot is still blank, can someone please tell me how to get something to show up in my plot

[Image Analyst]

Figure out what? How to use the debugger? See this link

To get something to show up in your plot, use the plot() function. That's about all we can say unless we see your code. If you want more help, read this first then start a new question.

[Michael Roberts]

to clarify: i have gotten this far in my code, but my plot is still empty. my code is

A = [ 0 0 0.43; 0.6 0 0; 0 0.75 0.96 ];

T = [ 1 2 3 4 5 10 20 25 50 75 ];

V0 = [ 42, 0, 95 ]'; 
V=zeros(3,length(T)); 
V(:,1)=V0; 
i=0; 
for t=T 
i=i+1; 
V(:,1)=(A^t)*V0; 
end

figure

T=[0 1 2 3 4 5 10 20 25 50 75];

%legend('calves','yearlings','adults')

title('population versus time')

xlabel('time')

ylabel('population')

I just can't figure out why my plot is blank

[Walter Roberson]

A = [ 0 0 0.43; 0.6 0 0; 0 0.75 0.96 ];
T = [ 0 1 2 3 4 5 10 20 25 50 75 ];
V0 = [ 42, 0, 95 ]';
V=zeros(3,length(T));
for i = 1 : length(T)
      V(:,i)=(A^T(i))*V0;
end
figure
T2=log(T);
V2=log(V);
plot( T2, V2(1,:), 'b', T2, V2(2,:), 'g', T2, V2(3,:), 'r')
legend('calves','yearlings','adults')
title('population versus time')
xlabel('time')
ylabel('population')

[Image Analyst]

It's blank because you didn't use plot() like I recommended. Walter did use it and so his code does show data.

[Michael Roberts]

Thank you very much Walter and Mr. italicizing image analyst