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put me out of my misery

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Rizwana
Rizwana 2014-1-31
评论： Bjorn Gustavsson 2014-2-3
i have 3 matrices..
x = 1 * 264;
y = 1* 264;
z = 1 * 264;
contour(x,y,z) % error z must be 2* 2 or more
hence i did
[X,Y] = meshgrid(x,y); Z =griddata(x,y,z,X,Y);
contour(X,Y,Z) is giving some weird plot. Not desirable.
Now how to do it...
  2 个评论
Iain
Iain 2014-1-31
What are you trying to plot?
contour(x,y,z) is expecting x to be a vector with n elements, y a vector with m elements, and z to be n by m (or is it m by n)
Rizwana
Rizwana 2014-1-31
编辑：Rizwana 2014-1-31
my x is a 1 col,264 row matrix reading radius,y is 1 col,264 row matrix reading angles in degrees. and z is pressure gain 1* 264. I want to plot radius versus circumferential angle in degrees with contours of pressure. Thank you

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采纳的回答

Bjorn Gustavsson
Bjorn Gustavsson 2014-1-31
编辑：Bjorn Gustavsson 2014-1-31
First you have to get yourself a good overview of what you actually have, I suggest using scatter:
qwe = xlsread('yourfile.xls');
scatter(qwe(:,1).*cos(qwe(:,2)*pi/180),...
qwe(:,1).*sin(qwe(:,2)*pi/180),15,...
(qwe(:,3)-min(qwe(:,3)))*5+5,'filled')
So there you see some odd spots (sensor faulty or something?). At least easy to reinterpolate outside that region:
X = 24.7:0.1:27;
Y = 0:0.1:5;
[X,Y] = meshgrid(X,Y);
Z = griddata(qwe(:,1).*cos(qwe(:,2)*pi/180),...
qwe(:,1).*sin(qwe(:,2)*pi/180),qwe(:,3),X,Y);
% Or any of the newer variants like Walter suggested.
% do the contour:
hold on
contour(X,Y,Z,1.25:0.025:max(qwe(:,3)),'b')
HTH
  2 个评论
Rizwana
Rizwana 2014-2-3
编辑：Rizwana 2014-2-3
Than you for your help. Iam great full to you for teaching me so many things in simple 5 lines of codes:). Just one doubt... You have done radius* cos(theta) for qwe(:,1).*cos(qwe(:,2)*pi/180) and radius * sin(theta) for qwe(:,1).*sin(qwe(:,2)*pi/180)... While plotting do we should convert degrees into radian??? because you have multiplied it with pi/180?? Is it compulsory???
Bjorn Gustavsson
Bjorn Gustavsson 2014-2-3
Yes, the trigonometric functions work on radians. You'd be better off learning to use radians.

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更多回答（3 个）

Mischa Kim
Mischa Kim 2014-1-31
Rizwana, first option works just fine. Make sure that Z is an mxn matrix, where m and n are the length of the two vectors x and y. meshgrid , e.g., generates an appropriate grid.
x = rand(10,1);
y = rand(10,1);
[X,Y] = meshgrid(x,y);
Z = sin(X)+cos(X+Y);
figure
contour(X,Y,Z)
or see the documentation.
  3 个评论
显示 1更早的评论
Mischa Kim
Mischa Kim 2014-1-31
The contour plot is more of a 3D type plot, where the dependent variable (Z) depends on two variables (X, Y). So it is not quite clear to me what you would like to achieve.
Rizwana
Rizwana 2014-1-31
I will attach an excel file. 1st row is radius, 2nd row is circumferential angle in degrees and z is 3rd row whose contours i need to plot... This is just experimental data collected... are you trying to get idea of what iam trying to plot???

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Iain
Iain 2014-1-31
编辑：Iain 2014-1-31
Looks like you actually want: plotyy or subplots:
plotyy(x,y,x,z) % plot angle against radius on the left hand y axis, and pressure against radius on the right hand y axis.
subplot(211)
plot(x,y)
subplot(212)
plot(x,z)
or
subplot(121)
plot(x,y)
subplot(122)
plot(x,z)
obviously, switch the x,y,z's around to plot against what you want to. - contour plots are only valid for 2-D signals, and you've only got 3 1D signals.
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Iain
Iain 2014-1-31
Is circumferential pressure supposed to be a function of angle and radius?
If radius has "n" elements, and you have "m" angles, then you should get "n x m" pressures, and not have all three as being vectors.
For example, with a trivial function I know is wrong:
x= 0:0.1:1;
y= 0:36:360;
z = x' * y;
contour(x,y,z)
would work.
Rizwana
Rizwana 2014-1-31
Its total pressure coefficient(z). In a turbine blade, pressure varies with radius and pitch variation... z is just set of data. Not a function.

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Walter Roberson
Walter Roberson 2014-1-31
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Walter Roberson
Walter Roberson 2014-1-31
It appears that TriScatteredInterp appeared in R2009a. griddata() does exist in your release though.
Rizwana
Rizwana 2014-2-3
Thank you. I will try downloading new 2013 version. Thank you very much for highlighting the other 2 functions i can use.

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