put me out of my misery

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...

[Iain]

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]

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

Answer 1

[Bjorn Gustavsson]

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

[Rizwana]

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]

Yes, the trigonometric functions work on radians. You'd be better off learning to use radians.

Answer 2

[Mischa Kim]

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.

[Rizwana]

My Z matrix is already defined as 1* 264 matrix. These are just set of 1 col readings 264 reading. I cant use Z = sin(X)+cos(X+Y) because Z is no where in my experiment related by that formula. Thank you.

[Mischa Kim]

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]

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???

Answer 3

[Iain]

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.

[Rizwana]

Nope i dont want to subplot.. I need contour of circumferential pressure(z=1*264 matrix) with radius on y-axis(1*264) and circumferential angle in degrees(1*264) on x-axis.. If i give you my data can you help me out..?

[Iain]

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]

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.

Answer 4

[Walter Roberson]

TriScatteredInterp or the new scatteredinterpolant

[Rizwana]

its giving me error saying

Undefined function or method 'scatteredInterpolant' for input arguments of type 'double'.

[Walter Roberson]

I did say it was new. Use TriScatteredInterp then.

[Rizwana]

x = rand(100,1)*4-2; y = rand(100,1)*4-2; z = x.*exp(-x.^2-y.^2); >> F = TriScatteredInterp(x,y,z);

??? Undefined function or method 'TriScatteredInterp' for input arguments of type 'double'.

[Walter Roberson]

Could you remind me of which MATLAB version you are using?

[Rizwana]

matlab 7.6.0(R2008a)

[Walter Roberson]

It appears that TriScatteredInterp appeared in R2009a. griddata() does exist in your release though.

[Rizwana]

Thank you. I will try downloading new 2013 version. Thank you very much for highlighting the other 2 functions i can use.