new to matlab. trying to plot simple line and not successful from a script file!

r=0.0;
z=0.1;
h=0.1;

for i=1:50
  p=sqrt((1+(2*z*(r))^2)/((1+(r)^2)+(2*z*(r))))
  r=r+h
end

plot(p,r)

title('tr function')

There is just a blank figure screen when i run this. help please!

[Abdullah Caliskan]

r=0:1:50;
z=0.1; h=0.1;
p=sqrt((1+(2.*z.*(r)).^2)./((1+(r).^2)+(2.*z.*(r))));
plot(p,r); title('tr function');

try this one

Answer 1

[Amit]

Here you go:

h = 0.1;
r = 0:0.1:0.1*50;
z = 0.1:0.1:1;
fileID = fopen('my_p_data.txt', 'wt');
rr = {'b','r','k','g','-','--',':','-.','-k','--k'};
legstr = {};
for i = 1:numel(z)
  p = sqrt((1+(2*z(i)*(r)).^2)./((1+(r).^2)+(2*z(i)*(r))));
  fprintf(fileID,'%f\n', p);
  plot(p,r,rr{i});
  legstr{i}= ['Z = ' num2str(z(i))];
  hold on;
end
fclose(fileID);
title('tr function')
legend(legstr);

Answer 2

[Amit]

This might work.

h = 0.1;
r = 0:0.1:0.1*50;
z = 0.1;
p = sqrt((1+(2*z*(r)).^2)./((1+(r).^2)+(2*z*(r))));
plot(p,r)
title('tr function')

The reason it was not plotting anything cause once you get out of the loop, you had a single value for p and r, and you cannot plot a line using a single value!

Answer 3

[Praketa]

ok it worked but i wanted to know how we can use the fid() function, store data in txt file and reload to output while utilizing the loops. i have a c++ background so it is easier for me to follow that logic. the matrix operations are confusing for now.

and i also want to vary the z variable and from 0.1 to 1. if i use this then I am getting unmatched dimensions error.

i saw on some forum to load this data into txt file...does anybody know about that!

[Amit]

I am lost? what do you mean by 'reload to output'?

[Praketa]

fine lets work with this right now...what if i want to vary z as well but from 0.1 to 1, apart from r. wont i have a dimensions mismatch. actually i tried and it did

[Amit]

h = 0.1;
r = 0:0.1:0.1*50;
z = 0.1:0.1:1;
fileID = fopen('my_p_data.txt', 'wt');
for i = 1:numel(z)
  p = sqrt((1+(2*z(i)*(r)).^2)./((1+(r).^2)+(2*z(i)*(r))));
  fprintf(fileID,'%f\n', p);
  plot(p,r)
  hold on;
end
fclose(fileID);
title('tr function')

In every loop, the new value of z (0.1,0.2 ... 1) is used.

and you can use Image Analyst way to store p generated in every loop.

[Amit]

h = 0.1;
r = 0:0.1:0.1*50;
z = 0.1:0.1:1;
fileID = fopen('my_p_data.txt', 'wt');
for i = 1:numel(z)
  p = sqrt((1+(2*z(i)*(r)).^2)./((1+(r).^2)+(2*z(i)*(r))));
  fprintf(fileID,'%f\n', p);
  figure;
  plot(p,r)
end
fclose(fileID);
title('tr function')

Answer 4

[Image Analyst]

Did you look at the documentation for fprintf. Here's an example:

x = 0:.1:1;
A = [x; exp(x)];

fileID = fopen('exp.txt','w');
fprintf(fileID,'%6s %12s\n','x','exp(x)');
fprintf(fileID,'%6.2f %12.8f\n',A);
fclose(fileID);

For your case

fileID = fopen('my_p_data.txt', 'wt');
fprintf(fileID,'%f\n', p); % Write p out to a file.
fclose(fileID);

Answer 5

[Praketa]

thank you much everybody for the help so far. but i wanted different graphs showing influence of z and the above code only outputs one graph!

[Amit]

I have edited the code to give you different plots with changing z

Answer 6

[Praketa]

Amit loads of thanks. but almost. can i have these figures all in in single figure. i want my students to see the relation. anyhow i can recommend ur skills I would be glad to.

[Praketa]

any different graphs i meant all the graphs with different z values but in the same figure

Answer 7

[Praketa]

u r awesome amit! thanks a ton!