MATLAB: Plotting graph with uneven amount of vectors

plotunevenvectors

Hello everyone,

So, I want to plot a graph pressure over volume. Both values have been measured over a time of 0.85 seconds, however the pressure has been recorded at a 170 moments and the volume has been recorded at only 69 moments. How can I make this work?

Best Answer

take the later of the two start times and the earlier of the two end times. linspace some points between the two. interp1 the pressure at those query points and the temperature at those query points . Now you can plot the interpolated values against each other .

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MATLAB: How to identify corners of data plotted to estimate data between corners

How about using interp1 with the 'pchip' option? You did speculate the interpolation is overly complex, but then again it is only one line in Matlab.

First I generate some (fake) data similar to what you have shown.

y = @(x) 320*(1+tanh(x-5));
x = linspace(0,8)';
Ts = 1; % [s] 
xi = [0:Ts:8]'; 
[xs,ys] = stairs(xi, y(xi))
plot(x,y(x), xs, ys, xi, y(xi), 'rs')

Now the ZOH sample & held data is (xi, y(xi)). Using only this data, we reconstruct the higher density data with interp1.

Ts2 = Ts/10; 
xi2 = [0:Ts2:8]'; 
yq = interp1(xi, y(xi), xi2, 'pchip'); 
plot(xi, y(xi), 'rs', xi2, yq, 'b-')

I use the pchip option to avoid "wobbles" in the interpolation.

MATLAB: System of 3 equation with 3 unknown, with two 2nd order equation

The resuillts are strictly numerical (not containing symbolic variables), so use vpasolve instead of solve:

syms QV3 QV2 QVl
eqn1 = 17.79  == QV3 + QV2+QVl;
eqn2 = 0.25*QV3.^2 == 0.14 * QV2^2;
eqn3 = 0.25*QV3.^2 == 3.89* QVl^2;
sol = vpasolve([eqn1, eqn2, eqn3], [QV3 , QV2, QVl])
QV3Sol = sol.QV3
QV2Sol = sol.QV2
QVLsol = sol.QVl

producing:

QV3Sol =
 -214.86507282291207239983881906658
  6.8692131509642582629301134641865
 -30.161934858502498504240076448371
  8.5414023987755051080751389638705
 
QV2Sol =
  287.1255310312749278205504662485
 9.1793721884393279626540627283888
 40.305580843825110030042867255874
 11.413929063852511018159550534661
 
QVLsol =
 -54.470458208362855420711647181924
  1.7414146605964137744158238074247
  7.6463540146773884741972091924965
 -2.1653314626280161262346894985318

These are however still symbolic values. To use them in other calculations, convert them to double-precision values with the double function.

Best Answer

Related Solutions

MATLAB: How to identify corners of data plotted to estimate data between corners

MATLAB: System of 3 equation with 3 unknown, with two 2nd order equation

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