I am brand new to MATLab and do not know how to do a whileloop

x=0;
while (x<20)
    x=x+1
    f(x)= x^3 - (5*x)^2 + 2^(x) - 10000.*x;
fig=figure(1); clf; grid on; hold on;
     xlabel('x1'); ylabel('y1'); title('While Loop');
     p = plot(Value(:,1),Store(:,1));
     set(p,'Color','red','LineWidth',2);
end

what is wrong and why will it not plot? everything from fig=figure(1); on is given

Answer 1

[Image Analyst]

Lots of errors - too many to list. Just study corrected code:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 25;

fig=figure(1);
x(1)=0;
fx(1) = 0;
index = 2;
while (x<20) & index < 1000 % Add index check as a failsafe.
  x(index)=x(index-1)+0.5
  fx(index)= x(index)^3 - (5*x(index))^2 + 2^(x(index)) - 10000.*x(index);
  clf;
  grid on;
  hold on;
  xlabel('x', 'FontSize', fontSize); 
  ylabel('fx', 'FontSize', fontSize); 
  title('While Loop', 'FontSize', fontSize);
  p = plot(x, fx, 'ro-', 'LineWidth',2, 'MarkerSize', 10);
  index = index + 1;
end
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

Of course I hope you know you could do this without a while loop in just a few lines, but I guess you were interested in the while loop mechanics rather than just how to plot a curve.

[Nicholas]

thank you so much!! would it be about the same for a "for loop" just with a different equation?

[Image Analyst]

Here's the for loop version:

fig=figure(1);
x(1)=0;
fx(1) = 0;
index = 2;
for index = 2 : 100000
  x(index)=x(index-1)+0.5
  fx(index)= x(index)^3 - (5*x(index))^2 + 2^(x(index)) - 10000.*x(index);
  clf;
  grid on;
  hold on;
  xlabel('x', 'FontSize', fontSize); 
  ylabel('fx', 'FontSize', fontSize); 
  title('For Loop', 'FontSize', fontSize);
  p = plot(x, fx, 'ro-', 'LineWidth',2, 'MarkerSize', 10);
  % Exit loop if x >= 20
  if x(index) >= 20
    break;
  end
end
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

And here is the vectorized version:

x = 0 : 0.5 : 20;
fx = x.^3 - (5*x).^2 + 2.^x - 10000.*x;
p = plot(x, fx, 'ro-', 'LineWidth',2, 'MarkerSize', 10);
grid on;
hold on;
xlabel('x', 'FontSize', fontSize);
ylabel('fx', 'FontSize', fontSize);
title('Vectorized', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

[Andrew Reibold]

Were the first dozen lines in the original answer reeeeeally necessary or were you just trying to be impressive? x)

Font size to 25? lol

Still though, a good response with complete code as an example. Good work

[Nicholas]

how would i put a while loop and a for loop on the same graph if the for loop's function is f(x) = 20000*log(x)-3x I tried to almost repeat it like this

fig=figure(1);
x(1)=1;
fx(1)=-3;
for (x<20) & index < 1000
    x(index) = x(index)+1
    fx(index) = 20000*log(x(index)) - 3*x
    clf;
  grid on;
  hold on;
  xlabel('x', 'FontSize', 10); 
  ylabel('fx', 'FontSize', 10); 
  title('While Loop', 'FontSize',10);
  p = plot(x, fx, 'ro-', 'LineWidth',2, 'MarkerSize', 10);
  index = index + 1;
end

set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1])

and to just place in the while loop operation to give me something like this

fig=figure(1);
x(1)=0;
fx(1) = 0;
index = 2;
while (x<20) & index < 1000
  x(index)=x(index-1)+0.5
  fx(index)= x(index)^3 - (5*x(index))^2 + 2^(x(index)) - 10000.*x(index);
  fig=figure(1);
x(1)=1;
fx(1)=-3;
for (x<20) & index < 1000
    x(index) = x(index)+1
    fx(index) = 20000*log(x(index)) - 3*x
    clf;
  grid on;
  hold on;
  xlabel('x', 'FontSize', 10); 
  ylabel('fx', 'FontSize', 10); 
  title('While Loop', 'FontSize',10);
  p = plot(x, fx, 'bo-', 'LineWidth',2, 'MarkerSize', 10);
  index = index + 1;
    clf;
  grid on;
  hold on;
  xlabel('x', 'FontSize', 10); 
  ylabel('fx', 'FontSize', 10); 
  title('While Loop', 'FontSize',10);
  p = plot(x, fx, 'ro-', 'LineWidth',2, 'MarkerSize', 10);
  index = index + 1;
end

set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1])

but that was wrong.. How can I place them both on one graph?

[Image Analyst]

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 25;
x(1)=0;
fx(1) = 0;
index = 2;
while (x<20) & index < 1000 % Add index check as a failsafe.
  x(index)=x(index-1)+0.5;
  fx(index)= x(index)^3 - (5*x(index))^2 + 2^(x(index)) - 10000.*x(index);
  p = plot(x, fx, 'ro-', 'LineWidth',2, 'MarkerSize', 10);
  index = index + 1;
end
grid on;
hold on;
xlabel('x', 'FontSize', fontSize);
ylabel('fx', 'FontSize', fontSize);
title('While Loop', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

x2(1)=0;
fx2(1) = 0;
index = 2;
for index = 2 : 100000
  x2(index)=x2(index-1)+0.5;
  fx2(index) = 20000*log(x2(index)) - 3*x2(index);
  p = plot(x2, fx2, 'bo-', 'LineWidth',2, 'MarkerSize', 5);
  % Exit loop if x >= 20
  if x(index) >= 20
    break;
  end
end
grid on;
xlabel('x', 'FontSize', fontSize);
ylabel('fx', 'FontSize', fontSize);
title('Both Loop', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);