How to plot imported data into matlab equations

Kiaora MatLAB community

Below I have an equation defined as T. However, I do not know how to import the data into the equation and plot it.

syms omega mu epsilon sigma
k1 = omega .* sqrt((mu .* epsilon)/(2)) .* sqrt(sqrt(1 + ((sigma)/(epsilon .* omega))^2) + 1);
k2 = omega .* sqrt((mu .* epsilon)/(2)) .* sqrt(sqrt(1 + ((sigma)/(epsilon .* omega))^2) - 1);
k = k1 + 1i.*k2;

Z_0 = 377;
Z_b = sqrt(1/9.3) .* Z_0;

T = @(h) - (((4 .* exp(1i .* k .* h)) .* Z_0 .* Z_b)/((-Z_0)^2 + (exp(2i .* k .* h) .* (Z_0)^2) - 2 .* Z_0 .* Z_b - (2 .* exp(2i .* k .* h) .* Z_0 .* Z_b) - (Z_b)^2 + exp(2i .* k .* h) .* (Z_b)^2));
A = T(0);
B = abs(T./A);
theta = angle(T./A);

h = readtable('height.xlsx');
plot(h.Height(1:10,1),T)

Error using plot
Invalid data argument.

I want to plot T against h. I used readtable but not sure if that is enough for the plot to show up.

Please help

[Chunru]

You need to specify omega mu epsilon sig in order to evaluate T.

[Aloe]

@Chunru What if I want them as constants? I was told to use syms if I want them as constants

[Walter Roberson]

Aloe, you flagged this as a duplicate. What is the link to the other (earlier) version of the question that you think this is a duplicate of?

Answer 1

[Walter Roberson]

syms omega mu epsilon sigma

Symbolic variables.

k1 = omega .* sqrt((mu .* epsilon)/(2)) .* sqrt(sqrt(1 + ((sigma)/(epsilon .* omega))^2) + 1);
k2 = omega .* sqrt((mu .* epsilon)/(2)) .* sqrt(sqrt(1 + ((sigma)/(epsilon .* omega))^2) - 1);

So k1 and k2 are defined in terms of the symbolic variables epsilon, mu, omega, sigma

k = k1 + 1i.*k2;

and k is therefore defined in terms of them as well

T = @(h) - (((4 .* exp(1i .* k .* h)) .* Z_0 .* Z_b)/((-Z_0)^2 + (exp(2i .* k .* h) .* (Z_0)^2) - 2 .* Z_0 .* Z_b - (2 .* exp(2i .* k .* h) .* Z_0 .* Z_b) - (Z_b)^2 + exp(2i .* k .* h) .* (Z_b)^2));

T is defined as an anonymous function that invokves k and h and some numeric constants, so that means that T is an anonymous function involving symbolic variables epsilon, mu, omega, sigma and input variable h

A = T(0);
B = abs(T./A);

T(0) would evaluate function handle T passing in 0 for h. The result would normally be in terms of the symbolic variables epsilon, mu, omega, sigma but because you are multiplying k by h = 0, the symbolic variables all vanish, so A should be independent of the symbolic variables.

You then try to divide the handle to the anonymous function T by that value. You cannot divide a function handle by something. You could, though, do

B = @(h) abs(T(h)./A);

Then

theta = angle(T./A);

same problem, you cannot divide a function handle, but you could define

theta = @(h) angle(T(h)./A);

Then

plot(h.Height(1:10,1),T)

plot() does not accept the handle to an anonymous function. You could try

H = h.Height(1:10,1);
plot(H, T(H))

but... remember T involves the symbolic variables epsilon, mu, omega, sigma so evaluating T at a numeric location would return a symbolic expression in four symbolic variables.

An expression in four symbolic variables has four independent variables and one dependent result, and so requires a 5 dimensional plot in itself. But you have different h values, so really you have 5 independent variables and one dependent result, so you requires a 6 dimensional plot. It is very difficult to plot in 6 dimensions in a way that makes sense to humans, especially if you are doing a grid plot rather than a scattered plot.

[Aloe]

@Walter Roberson If I were to use

plot(H, T(H))

then does that mean that I need to change all the h used in the code to H?

[Walter Roberson]

No!

You have

h = readtable('height.xlsx');

so your h variable is a table object. But you need to apply the function to some data stored in the table, h.Height(1:10) so it is most efficient to extract that data into a variable and use the variable.

If it would confuse you less, you could use

plot(h.Height(1:10,1), T(h.Height(1:10,1)))

Answer 2

[Paul]

One way that uses symbolic (which isn't really necessaray)

syms omega mu epsilon sigma h
k1 = omega .* sqrt((mu .* epsilon)/(2)) .* sqrt(sqrt(1 + ((sigma)/(epsilon .* omega))^2) + 1);
k2 = omega .* sqrt((mu .* epsilon)/(2)) .* sqrt(sqrt(1 + ((sigma)/(epsilon .* omega))^2) - 1);
k = k1 + 1i.*k2;
Z_0 = 377;
Z_b = sqrt(1/9.3) .* Z_0;
T =  - (((4 .* exp(1i .* k .* h)) .* Z_0 .* Z_b)/((-Z_0)^2 + (exp(2i .* k .* h) .* (Z_0)^2) - 2 .* Z_0 .* Z_b - (2 .* exp(2i .* k .* h) .* Z_0 .* Z_b) - (Z_b)^2 + exp(2i .* k .* h) .* (Z_b)^2));
T = matlabFunction(T)

T = function_handle with value:
    @(epsilon,h,mu,omega,sigma)(exp(-h.*(omega.*sqrt(sqrt(1.0./epsilon.^2.*1.0./omega.^2.*sigma.^2+1.0)-1.0).*sqrt((epsilon.*mu)./2.0)-omega.*sqrt(sqrt(1.0./epsilon.^2.*1.0./omega.^2.*sigma.^2+1.0)+1.0).*sqrt((epsilon.*mu)./2.0).*1i)).*(-1.864237404282749e+5))./(exp(-h.*(omega.*sqrt(sqrt(1.0./epsilon.^2.*1.0./omega.^2.*sigma.^2+1.0)-1.0).*sqrt((epsilon.*mu)./2.0).*2.0-omega.*sqrt(sqrt(1.0./epsilon.^2.*1.0./omega.^2.*sigma.^2+1.0)+1.0).*sqrt((epsilon.*mu)./2.0).*2.0i)).*6.419981795790556e+4+3.363444161381954e+4)

T(1,[1; 2],1,1,1)  % example

ans = 
  -4.1023 - 1.0533i
   1.8974 - 1.3832i

Now T is an anonymous function that can be evaluated for values of its input arguments. If that doesn't work, becaus of overflow or something, then the full symbolic approach would be

syms T
T(h,epsilon,mu,omega,sigma) =  - (((4 .* exp(1i .* k .* h)) .* Z_0 .* Z_b)/((-Z_0)^2 + (exp(2i .* k .* h) .* (Z_0)^2) - 2 .* Z_0 .* Z_b - (2 .* exp(2i .* k .* h) .* Z_0 .* Z_b) - (Z_b)^2 + exp(2i .* k .* h) .* (Z_b)^2));

which can be evaluated for values of the inputs arguments

T([1;2],1,1,1,1)

ans = 

vpa(ans)

ans = 

[Aloe]

@Paul I tried inputting my data to the varible h using this but not getting anything

[Paul]

Please show the complete code. Inclulde any error messages that result from running the code.