Looping a program or multiple variables?

Hi,

I'm trying to determine the probability of a basketball shooting at the hoop on a correct line. Really basic at the moment, a line y=mx+c changes from a given point depending on the players shot angle phi.

I would like to run the program 100 times so that I can say player got ball on line x amount of times out of 100.

At the moment I am using the following code:

%Finding the maximum and minimum points of entering the hoop
%Initial launch data
x0=20;
y0=4;

    n = 100;
  q = randn(1,n)

    mean_phi=atand((7.5-y0)/(26.425-x0));
  sd_phi=2;
  phi=mean_phi+sd_phi*q

    %Gradient m given by
  m=tand(phi)
  %Constant c given as
  c=y0-m*x0

    %Using the quadratic formula
  a=((m.^2)+1);
  b=2*m*(c'-7.5)-52.85;
  d=698.281+((c'-7.5).^2)-0.01;

    %Find the coordinates of intersection if possible
  if ((b.^2)-4*a*d)>0
      xp=(-b+sqrt((b.^2)-(4*a*d)))/(2*a')
      xm=(-b-sqrt((b.^2)-(4*a*d)))/(2*a')
      yp=m*xp'+c
      ym=m*xm'+c
  else
      fprintf('The ball missed the hoop\n')
  end

    %Ball enters hoop if ball lands between (xm,ym) and (xp,yp)
  o=(27-x0)/99
  x=x0:o:27;
  y=(m'*x)+c;

    plot (x,y)

But right at the end when I want to plot a graph between the players position an x =27, the straight equation has matrices that don't match.

would it be better to loop the program using i=100 or can someone see a glaring error in my code.

Any help would be much appreciated.

Cheers

Stu

[Walter Roberson]

Consider using

x = linspace(x0, 27, 100);

instead of your current "o" and "x" code.

[Stuart]

Thanks walter, but do you have any idea about the random iteration part?

Answer 1

[Sargondjani]

you should keep it in vectorized form, unless you are really new to matlab as looping is usually easier to follow/debug

about your error: if the sizes of the matrices don't match, and you expected them to match, then you just have to figure out why they differ. really that simple...

you can do [rows_X,cols_X]=size(X) to determine the size of a variable in every step... see where it goes wrong

[Stuart]

Having read through my code and your answer, I think I've confused myself with what I want to achieve.

I would like 100 plotted lines of form y=mx+c where x is always between x0 and 27. The things that change are m and c, however they are paired together, as you can see in my code, c is determined by m.

So do I have to perform the loop in a different way?

[Sargondjani]

i hate decoding matlab code, so can you tell where you want the 100 lines for:

100 draws of phi

or

100 different 'starting values' for x