Asked by Tom
on 15 Nov 2018

I am working on a problem in mechanics and have obtained an expression for the force on an object: the expression contains several constants and a parameter. In the code elsewhere I have stated that this parameter just has an arbitrary value of 1 after dimensionalisation, but I need to now allow it to vary from 0 to 1 and plot the expression as a function on a graph depending on the parameter, what would be the easiest way of doing this?

I know MATLAB has a plot(X,Y) function, but obviously this will not work immediately as I have already fixed the parameter essentially arbitrarily just to obtain a numerical value which I can compare with other expressions.

Answer by madhan ravi
on 15 Nov 2018

Edited by madhan ravi
on 15 Nov 2018

Accepted Answer

how about this example: (if it doesn't work provide your code and datas)

syms x(t)

x(t)=t*exp(t-1)

fplot(x(t),[0 1]) % ranging from 0 to 1

madhan ravi
on 16 Nov 2018

if my answer worked make sure to accept the answer

Tom
on 16 Nov 2018

It didn't work, I get a function which doesn't look right.

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Answer by Tom
on 15 Nov 2018

I'm not sure if that will work, I will give an example of the code to see if that helps. Basically, there is a parameter Kn which I set to 1 in the course of finding the solution which gives the force on an object. I have a function which features Kn which is evaluated numerically at various grid points.

function [V]=StokesletEval(rij,normal)

Kn=1;

J=1/(8*pi*Kn)*(eye(3)/norm(rij)+(rij'*rij)/((norm(rij))^3));

K=(-1/(4*pi))*(rij'*normal*(eye(3)/norm(rij)^3-3*(rij'*rij)/norm(rij)^5)*(eye(3)-normal'*normal));

V=(J+sqrt(pi/2)*K);

end

Evaluating the function at the grid and solving the system which results you get the total force (or drag) called dragFZ. I then divide the result by -6*pi*VZ*Kn, another equation which depends on Kn. Although I have assumed Kn=1, I somehow need to take that ratio and plot the result against Kn, as Kn varies from 0 to 1. I have tried the following (where I called Kn t):

syms x(t)

x(t)=dragFZ/(-6*pi*VZ*t);

fplot(x(t),[0 1])

but the graph does come out as expected.

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