Using parametric equations in terms of theta1 and theta2 to plot a point A for a range of angles

I am trying to write a code that uses two parametric equations of x and y, which depend on the variables theta1 and theta2. Then I have to produce a plot of x Vs y for a range of values of theta1 and theta2. I am stuck how can I do this?

Bellow is my current code to display the coordinate of this point defined by the parametric equations a and b (btw this code doesn't work for reasons that I do not understand). Now I have to use these functions to produce an array that will plot the x,y coordinates over a range of values of theta1 (20 to 80 deg in increments of 0,5) and of theta2 (90 to 30 deg in increments if 0,5).

Thanks in advance for any help! Started Matlab a few weeks ago :) (I attached a screenshot of the question)

n1 = input('Enter θ1: '); 
n2 = input('Enter θ2: ');

function a = first_calc(n1,n2)
    a = 0.6*cosd(n1) + 0.2*cosd(n1-n2);
end

function b = second_calc(n1,n2)
    b = 0.6*sind(n1) + 0.2*sind(n1-n2);
end

fprintf('The value for x is %g, and that of y is g%\n' a,b);

Answer 1

[Krishna Zanwar]

Hey Raphael,

In this case you have defined a function but not called it in your script and so you are getting an error while printing the a and b variables.

You can just call the function in your script as

a = first_calc(n1,n2);
b = second_calc(n1,n2);

You can get the example on it here.

Secondly to create an array –

Theta1=20:0.5:80;
Theta2=90:-0.5:30;

You can learn how to use the plot function here.

[Raphael Aubry]

Hello Krishna

I have modified my code following your answer, I called my function in the script, created an array for the theta1/2, and also used a for loop to be able to plot my function, however, do I simply call my functions within the loop one after the other, or do I use the syntax "function // end" for each of the two functions within that loop like this?:

i = 1 
for theta1=20:0.5:80;
    theta2=90:-0.5:30;
    
    function a(i) = first_calc(theta1, theta2)
                i = i + 1
    end

    function b(i) = second_calc(theta1,theta2)
                i = i + 1
    end
end
    theta1 = [20:0.5:80];
    theta2 = [90:-0.5:30];
    
a = 0.6*cosd(theta1) + 0.2*cosd(theta1-theta2);
b = 0.6*sind(theta1) + 0.2*sind(theta1-theta2);


plot(a,b) 
xlabel('x Coordinate of Point A');
ylabel('Y Coordinate of Point A');

Also, since I am plotting the coordinate x and y using two seperate functions that calculate x and y from two inputs, is the syntax the same as it would be with only one function and an input? I have done it that way here but it does not run it

Thanks a lot for your time!

[Raphael Aubry]

My code is running! hopefully it is running propely but thanks a lot!

Here's my code for anyone who also needs help:

theta1=20:0.5:80;
theta2=90:-0.5:30;

function    a = first_calc(theta1, theta2)
            b = second_calc(theta1,theta2);
end

a = 0.6*cosd(theta1) + 0.2*cosd(theta1-theta2);
b = 0.6*sind(theta1) + 0.2*sind(theta1-theta2);

plot(a,b) 
xlabel('x Coordinate of Point A');
ylabel('Y Coordinate of Point A');

[Krishna Zanwar]

If you remove the function form there it will still work the same.

[Raphael Aubry]

I removed the function form and it says error, with the following message:

Error: File: first_calc.m Line: 13 Column: 1
Function definitions in a script must appear at the end of the file.
Move all statements after the "second_calc" function definition to before the first local function definition.

Error in MATLAB_COURSEWORK_Q2 (line 6)
a = first_calc(theta1, theta2)

[Krishna Zanwar]

I meant just put this in the script .

theta1=20:0.5:80;
theta2=90:-0.5:30;
a = 0.6*cosd(theta1) + 0.2*cosd(theta1-theta2);
b = 0.6*sind(theta1) + 0.2*sind(theta1-theta2);
plot(a,b) 
xlabel('x Coordinate of Point A');
ylabel('Y Coordinate of Point A');

It will give you the same response.

[Raphael Aubry]

Hey thanks a lot Krishna! it works very well now - things need to be kept very simply it seems and then it works. Bellow is a photo of the code and graph

Answer 2

[Krishna Zanwar]

Hey Raphael,

Since Matlab does direct calculations of Vectors you dont need a for loop for this problem.

theta1=20:0.5:80;
theta2=90:-0.5:30;
a = 0.6*cosd(theta1) + 0.2*cosd(theta1-theta2)
b = 0.6*sind(theta1) + 0.2*sind(theta1-theta2)

Hope it helps.