Wrong with matrix dimensions
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I'm only a beginner when it comes to MatLab and would therefor appreciate some help.
This is my code:
clc
clear
close all
load geiger.txt;
load temperatur.txt; %hämtar filerna med relevant data
i = geiger(:,4);
j = i*4500;
t1 = geiger(:,1);
x = [1:120]; %omvandling till rätt vektor
tidW = (x-1)*10;%omvandling till rätt enhet
t2 = temperatur(:,1);
tidT = (t2-1)*10;
T = temperatur(:,4)+273;
acc(1) = j(1);
for h = 2:length(j) %lägger ihop pulserna från geigermätaren
acc(h)= acc(h-1)+j(h);
end
p1 = polyfit(tidW,acc,3); %anpassar polynom till W(t)
pv1 = polyval(p1,tidW); %gör om värdena med polynomet som grund
pd1 = polyder(pv1); %deriverar polynomet
p = polyval(pd1, tidW)
p2 = polyfit(t2,T,2); %anpassar polynomet T(t)
pv2 = polyval(p2,t2);
pd2 = polyder(p2);
p2 = polyval(pd2,t2);
PH = 10*4190*p2;
e = PH./p;
plot(tidW,acc,'r')
hold on
plot(tidW, pv1,'b')
figure(2)
plot(t2, T,'r')
hold on
plot(t2,pv2,'b')
figure(3)
plot(t2,e)
And MatLab tells me that there's wrong with the matrix dimensions (matrix dimensions must agree)
This is due on tuesday and I'm getting a bit stressed out! All sort of help is highly appreciated!
采纳的回答
Matt Tearle
2011-2-18
0 个投票
I assume the error is at the bolded line ( e = PH./p ). It looks like this is due to a row vs column issue (as Walter mentions).
PH comes from p2, which comes from t2, which appears to be a column vector ( t2 = temperatur(:,1); ). So PH should be a column.
p however comes from tidW, which comes from x, which is a row vector ( x = [1:120]; ).
So you're trying to do an element-wise divide of a column by a row. No can do. Try simply transposing x to a column: x = (1:120)';
6 个评论
Lisa
2011-2-18
Matt Tearle
2011-2-19
Maybe, but not necessarily. Size in MATLAB means both rows and columns, so a row vector and column vector are different sizes, even if they have the same number of elements.
Can you please copy and post the error message you're getting, so we can see exactly which variables and which line of code it's referring to.
Also, please post the output from the command >> whos This is a useful diagnostic, if you don't know of it. It shows all your variables and their sizes.
Size matching issues are probably about the second most common error messages in MATLAB, so it's good to know how to track them down. Interactively, you can look at the workspace. At the command line, use the whos command.
Lisa
2011-2-19
Matt Tearle
2011-2-19
Yep, same issue: acc is a row, tidW is a column. See my other answer for a better way to calculate acc that also keeps it the same size as j (or just transpose it).
Lisa
2011-2-19
Matt Tearle
2011-2-19
You're very welcome. Can you accept and/or vote for answers that helped, so others know this has been solved (and what the solution was). Thanks. Open a new question if you keep having problems with the plot.
更多回答（2 个）
Walter Roberson
2011-2-18
0 个投票
Which line is it complaining about, and what are the sizes of the variables involved?
I notice that most of your variables are column vectors. However, because your acc array does not have a preallocated size, it will default to being a row vector. There are certainly cases where the difference between row vector and column vector could cause problems.
Matt Tearle
2011-2-18
Aside: you can replace
acc(1) = j(1);
for h = 2:length(j) %lägger ihop pulserna från geigermätaren
acc(h)= acc(h-1)+j(h);
end
with
acc = cumsum(j);
Oh yeah baby!
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