error?
显示 更早的评论
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')
1 个评论
Image Analyst
2011-11-22
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
采纳的回答
Walter Roberson
2011-11-22
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 ];
10 个评论
Image Analyst
2011-11-22
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
2011-11-22
Walter Roberson
2011-11-22
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
2011-11-22
Haley
2011-11-22
Walter Roberson
2011-11-22
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
2011-11-23
Haley
2011-11-23
Haley
2011-11-23
Walter Roberson
2011-11-23
Replace
V(:,1)=(A^t)*V0;
with
V(:,i)=(A^t)*V0;
and, of course, restore your plot() command.
更多回答（2 个）
Image Analyst
2011-11-22
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.
4 个评论
Haley
2011-11-22
Haley
2011-11-22
Image Analyst
2011-11-22
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
2011-11-22
Haley
2011-11-23
0 个投票
8 个评论
Image Analyst
2011-11-23
Yes, the debugger can be a more powerful tool than "Answers." Glad you learned how to use it.
Michael Roberts
2017-4-5
please help; how did you figure it out?
Michael Roberts
2017-4-5
my plot is still blank, can someone please tell me how to get something to show up in my plot
Image Analyst
2017-4-5
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
2017-4-5
编辑：Walter Roberson
2017-4-5
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
2017-4-5
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
2017-4-5
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
2017-4-5
Thank you very much Walter and Mr. italicizing image analyst
类别
在 帮助中心 和 File Exchange 中查找有关 Annotations 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
