I'm very very new to Matlab and I tried to attempt at making a simple iteration script.
Basically all I wanted to do was plot:
1*sin(x)
2*sin(x)
3*sin(x)
...
4*sin(x)
And this is the program that I wrote:
function test1
x=1:0.1:10;
for k=1:1:5;
y=k*sin(x);
plot(x,y);
end % /for-loop
end % /test1
However, it only plots y=5*sin(x) or whatever the last number is...
Any ideas?
Thanks!
Amit
You need to use the command hold on to make sure that the plot doesn't get erased each time you plot something new.
function test1
figure %# create a figure
hold on %# make sure the plot isn't overwritten
x=1:0.1:10;
%# if you want to use multiple colors
nPlots = 5; %# define n here so that you need to change it only once
color = hsv(nPlots); %# define a colormap
for k=1:nPlots; %# default step size is 1
y=k*sin(x);
plot(x,y,'Color',color(k,:));
end % /for-loop
end % /test1 - not necessary, btw.
EDIT
You can also do this without a loop, and plot a 2D array, as suggested by #Ofri:
function test1
figure
x = 1:0.1:10;
k = 1:5;
%# create the array to plot using a bit of linear algebra
plotData = sin(x)' * k; %'# every column is one k
plot(x,plotData)
Another option would be to use the fact the plot can accept matrices, and treats them as several lines to plot together.
function test1
figure %# create a figure
x=1:0.1:10;
for k=1:1:5;
y(k,:)=k*sin(x); %# save the results in y, growing it by a row each iteration.
end %# for-loop
plot(x,y); %# plot all the lines together.
end %# test1
Related
I am doing something similar to the following example:
t=linspace(0,1);
z=rand(1);
theta=pi*rand(1);
a_range=[1,2,3];
for nplot=1:3
a=a_range(nplot);
x=z*t.^2+a*sin(theta);
end
fname=['xsin.mat'];
save(fname)
the parameter a has three different values. For each value of a, I want to plot the function in one single figure. So at the end I will have three figures. I can do it using subplot but this will generate three plots in one figure which is not what I want.
In a new script, I load the mat file:
load('xsin.mat')
for nplot=1:3
figure(nplot)
plot(t,x)
end
but I get one figure not three as I should have. I mean for a=1, I should plot the curve in figure 1; for a=2, I should plot the curve in figure 2 and so on. How can I do this? Any help is appreciated.
You are overwriting x in every iteration; you could modify your code by saving each x for the respective nplot in a separate column of a matrix X (with minimal changes to your code):
t=linspace(0,1);
z=rand(1);
theta=pi*rand(1);
a_range=[1,2,3];
X = NaN(length(t), length(a_range)); % Create matrix to hold x values
for nplot=1:3
a = a_range(nplot);
x = z * t.^2 + a * sin(theta);
X(:,nplot) = x; % Store x in column of X
end
fname=['xsin.mat'];
save(fname)
Then, to create the figures:
load('xsin.mat')
for nplot=1:3
x = X(:,nplot); % Retrieve x from column of X
figure(nplot)
plot(t,x)
end
I have matrices x1, x2, ... containing variable number of row vectors.
I do successive plots
figure
hold all % or hold on
plot(x1')
plot(x2')
plot(x3')
Matlab or octave normally iterates through ColorOrder and plot each line in different color. But I want each plot command to start again with the first color in colororder, so in default case the first vector from matrix should be blue, second in green, third in red etc.
Unfortunately I cannot find any property related to the color index niether another method to reset it.
Starting from R2014b there's a simple way to restart your color order.
Insert this line every time you need to reset the color order.
set(gca,'ColorOrderIndex',1)
or
ax = gca;
ax.ColorOrderIndex = 1;
see:
http://au.mathworks.com/help/matlab/graphics_transition/why-are-plot-lines-different-colors.html
You can shift the original ColorOrder in current axes so that the new plot starts from the same color:
h=plot(x1');
set(gca, 'ColorOrder', circshift(get(gca, 'ColorOrder'), numel(h)))
plot(x2');
You can wrap it in a function:
function h=plotc(X, varargin)
h=plot(X, varargin{:});
set(gca, 'ColorOrder', circshift(get(gca, 'ColorOrder'), numel(h)));
if nargout==0,
clear h
end
end
and call
hold all
plotc(x1')
plotc(x2')
plotc(x3')
Define a function that intercepts the call to plot and sets 'ColorOrderIndex' to 1 before doing the actual plot.
function plot(varargin)
if strcmp(class(varargin{1}), 'matlab.graphics.axis.Axes')
h = varargin{1}; %// axes are specified
else
h = gca; %// axes are not specified: use current axes
end
set(h, 'ColorOrderIndex', 1) %// reset color index
builtin('plot', (varargin{:})) %// call builtin plot function
I have tested this in Matlab R2014b.
I found a link where a guy eventually solves this. He uses this code:
t = linspace(0,1,lineCount)';
s = 1/2 + zeros(lineCount,1);
v = 0.8*ones(lineCount,1);
lineColors = colormap(squeeze(hsv2rgb(t,s,v)))
ax=gca
ax.ColorOrder = lineColors;
Which should work for you assuming each of your matrices has the same number of lines. If they don't, then I have a feeling you're going to have to loop and plot each line separately using lineColors above to specify an RBG triple for the 'Color' linespec property of plot. So you could maybe use a function like this:
function h = plot_colors(X, lineCount, varargin)
%// For more control - move these four lines outside of the function and make replace lineCount as a parameter with lineColors
t = linspace(0,1,lineCount)'; %//'
s = 1/2 + zeros(lineCount,1);
v = 0.8*ones(lineCount,1);
lineColors = colormap(squeeze(hsv2rgb(t,s,v)));
for row = 1:size(X,1)
h = plot(X(row, :), 'Color', lineColors(row,:), varargin{:}); %// Assuming I've remembered how to use it correctly, varargin should mean you can still pass in all the normal plot parameters like line width and '-' etc
hold on;
end
end
where lineCount is the largest number of lines amongst your x matrices
If you want a slightly hacky, minimal lines-of-code approach perhaps you could plot an appropriate number of (0,0) dots at the end of each matrix plot to nudge your colourorder back to the beginning - it's like Mohsen Nosratinia's solution but less elegant...
Assuming there are seven colours to cycle through like in matlab you could do something like this
% number of colours in ColorOrder
nco = 7;
% plot matrix 1
plot(x1');
% work out how many empty plots are needed and plot them
nep = nco - mod(size(x1,1), nco); plot(zeros(nep,nep));
% plot matrix 2
plot(x2');
...
% cover up the coloured dots with a black one at the end
plot(0,0,'k');
Generate a plot showing the graphs of
y=(2*a+1)*exp(-x)-(a+1)*exp(2*x)
in the range x ∈ <-2, 4> for all integer values of a between -3 and 3
I know how to make typical plot for 2 values and set a range on the axes, but how to draw the graph dependent on the parameter a?
To elaborate on Ben Voigt's comment: A more advanced technique would be to replace the for-loop with a call to bsxfun to generate a matrix of evaluations of M(i,j) = f(x(i),a(j)) and call plot with this matrix. Matlab will then use the columns of the matrix and plot each column with individual colors.
%%// Create a function handle of your function
f = #(x,a) (2*a+1)*exp(-x)-(a+1)*exp(2*x);
%%// Plot the data
x = linspace(-2, 4);
as = -3:3;
plot(x, bsxfun(f,x(:),as));
%%// Add a legend
legendTexts = arrayfun(#(a) sprintf('a == %d', a), as, 'uni', 0);
legend(legendTexts, 'Location', 'best');
You could also create the evaluation matrix using ndgrid, which explicitly returns all combinations of the values of x and as. Here you have to pay closer attention on properly vectorizing the code. (We were lucky that the bsxfun approach worked without having to change the original f.)
f = #(x,a) (2*a+1).*exp(-x)-(a+1).*exp(2*x); %// Note the added dots.
[X,As] = ndgrid(x,as);
plot(x, f(X,As))
However for starters, you should get familiar with loops.
You can do it using a simple for loop as follows. You basically loop through each value of a and plot the corresponding y function.
clear
clc
close all
x = -2:4;
%// Define a
a = -3:3;
%// Counter for legend
p = 1;
LegendText = cell(1,numel(a));
figure;
hold on %// Important to keep all the lines on the same plot.
for k = a
CurrColor = rand(1,3);
y= (2*k+1).*exp(-x)-(k+1).*exp(2.*x);
plot(x,y,'Color',CurrColor);
%// Text for legend
LegendText{p} = sprintf('a equals %d',k);
p = p+1;
end
legend(LegendText,'Location','best')
Which gives something like this:
You can customize the graph as you like. Hope that helps get you started!
I need to produce a X vs Y graph and make a distinction between positive class and negative class (indicated in original data infile). How do I produce a legend in such a graph? This is my code for the graph right now :
infile = fopen('ClassData1.txt','r');
data = textscan(infile,'%f %f %f');
parameters = [data{1} data{2}];
label = [data{3}];
h = ones(100,9);
g = ones(100,9);
score1= ones(1,9);
sc = 0;
figure
for i = 1:100
if label(i)>0
plot(parameters(i,1),parameters(i,2),'r*')
hold on
else
plot(parameters(i,1),parameters(i,2),'b*')
end
end
To show each line type only once, you have to keep the handles. Storing only one handle per class is sufficient.
h=nan(2,1)
for i = 1:100
if label(i)>0
h(1)=plot(parameters(i,1),parameters(i,2),'r*')
hold on
else
h(2)=plot(parameters(i,1),parameters(i,2),'b*')
end
end
legend(h)
There are (more than) two ways to do this. Firstly, you can just use a single plot command and do the legend normally, by combining the plot definitions using logical indexing, or you can use the DisplayName property for each plot to give information about the legend.
% Some sample data
parameters=rand(100,2);
label=parameters(:,1)-0.5;
% Use logical indexing to replace the for loop and use a single plot command
figure(1)
plot(parameters(label>0,1),parameters(label>0,2),'r*',parameters(label<=0,1),parameters(label<=0,2),'b*')
legend('red','blue')
% Use DisplayName to set the legend entry for each plot, then show the legend using the names given
figure(2)
plot(parameters(label>0,1),parameters(label>0,2),'r*','DisplayName','Red')
hold on
plot(parameters(label<=0,1),parameters(label<=0,2),'b*','DisplayName','Blue')
hold off
legend('show')
for an implicit equation(name it "y") of lambda and beta-bar which is plotted with "ezplot" command, i know it is possible that by a root finding algorithm like "bisection method", i can find solutions of beta-bar for each increment of lambda. but how to build such an algorithm to obtain the lines correctly.
(i think solutions of beta-bar should lie in an n*m matrix)
would you in general show the methods of plotting such problem? thanks.
one of my reasons is discontinuity of "ezplot" command for my equation.
ok here is my pic:
alt text http://www.mojoimage.com/free-image-hosting-view-05.php?id=5039TE-beta-bar-L-n2-.png
or
http://www.mojoimage.com/free-image-hosting-05/5039TE-beta-bar-L-n2-.pngFree Image Hosting
and my code (in short):
h=ezplot('f1',[0.8,1.8,0.7,1.0]);
and in another m.file
function y=f1(lambda,betab)
n1=1.5; n2=1; z0=120*pi;
d1=1; d2=1; a=1;
k0=2*pi/lambda;
u= sqrt(n1^2-betab^2);
wb= sqrt(n2^2-betab^2);
uu=k0*u*d1;
wwb=k0*wb*d2 ;
z1=z0/u; z1_b=z1/z0;
a0_b=tan(wwb)/u+tan(uu)/wb;
b0_b=(1/u^2-1/wb^2)*tan(uu)*tan(wwb);
c0_b=1/(u*wb)*(tan(uu)/u+tan(wwb)/wb);
uu0= k0*u*a; m=0;
y=(a0_b*z1_b^2+c0_b)+(a0_b*z1_b^2-c0_b)*...
cos(2*uu0+m*pi)+b0_b*z1_b*sin(2*uu0+m*pi);
end
fzero cant find roots; it says "Function value must be real and finite".
anyway, is it possible to eliminate discontinuity and only plot real zeros of y?
heretofore,for another function (namely fTE), which is :
function y=fTE(lambda,betab,s)
m=s;
n1=1.5; n2=1;
d1=1; d2=1; a=1;
z0=120*pi;
k0=2*pi/lambda;
u = sqrt(n1^2-betab^2);
w = sqrt(betab^2-n2^2);
U = k0*u*d1;
W = k0*w*d2 ;
z1 = z0/u; z1_b = z1/z0;
a0_b = tanh(W)/u-tan(U)/w;
b0_b = (1/u^2+1/w^2)*tan(U)*tanh(W);
c0_b = -(tan(U)/u+tanh(W)/w)/(u*w);
U0 = k0*u*a;
y = (a0_b*z1_b^2+c0_b)+(a0_b*z1_b^2-c0_b)*cos(2*U0+m*pi)...
+ b0_b*z1_b*sin(2*U0+m*pi);
end
i'd plotted real zeros of "y" by these codes:
s=0; % s=0 for even modes and s=1 for odd modes.
lmin=0.8; lmax=1.8;
bmin=1; bmax=1.5;
lam=linspace(lmin,lmax,1000);
for n=1:length(lam)
increment=0.001; tolerence=1e-14; xstart=bmax-increment;
x=xstart;
dx=increment;
m=0;
while x > bmin
while dx/x >= tolerence
if fTE(lam(n),x,s)*fTE(lam(n),x-dx,s)<0
dx=dx/2;
else
x=x-dx;
end
end
if abs(real(fTE(lam(n),x,s))) < 1e-6 %because of discontinuity some answers are not correct.%
m=m+1;
r(n,m)=x;
end
dx=increment;
x=0.99*x;
end
end
figure
hold on,plot(lam,r(:,1),'k'),plot(lam,r(:,2),'c'),plot(lam,r(:,3),'m'),
xlim([lmin,lmax]);ylim([1,1.5]),
xlabel('\lambda(\mum)'),ylabel('\beta-bar')
you see i use matrix to save data for this plot.
![alt text][2]
because here lines start from left(axis) to rigth. but if the first line(upper) starts someplace from up to rigth(for the first figure and f1 function), then i dont know how to use matrix. lets improve this method.
[2]: http://www.mojoimage.com/free-image-hosting-05/2812untitled.pngFree Image Hosting
Sometimes EZPLOT will display discontinuities because there really are discontinuities or some form of complicated behavior of the function occurring there. You can see this by generating your plot in an alternative way using the CONTOUR function.
You should first modify your f1 function by replacing the arithmetic operators (*, /, and ^) with their element-wise equivalents (.*, ./, and .^) so that f1 can accept matrix inputs for lambda and betab. Then, run the code below:
lambda = linspace(0.8,1.8,500); %# Create a vector of 500 lambda values
betab = linspace(0.7,1,500); %# Create a vector of 500 betab values
[L,B] = meshgrid(lambda,betab); %# Create 2-D grids of values
y = f1(L,B); %# Evaluate f1 at every point in the grid
[c,h] = contour(L,B,y,[0 0]); %# Plot contour lines for the value 0
set(h,'Color','b'); %# Change the lines to blue
xlabel('\lambda'); %# Add an x label
ylabel('$\overline{\beta}$','Interpreter','latex'); %# Add a y label
title('y = 0'); %# Add a title
And you should see the following plot:
Notice that there are now additional lines in the plot that did not appear when using EZPLOT, and these lines are very jagged. You can zoom in on the crossing at the top left and make a plot using SURF to get an idea of what's going on:
lambda = linspace(0.85,0.95,100); %# Some new lambda values
betab = linspace(0.95,1,100); %# Some new betab values
[L,B] = meshgrid(lambda,betab); %# Create 2-D grids of values
y = f1(L,B); %# Evaluate f1 at every point in the grid
surf(L,B,y); %# Make a 3-D surface plot of y
axis([0.85 0.95 0.95 1 -5000 5000]); %# Change the axes limits
xlabel('\lambda'); %# Add an x label
ylabel('$\overline{\beta}$','Interpreter','latex'); %# Add a y label
zlabel('y'); %# Add a z label
Notice that there is a lot of high-frequency periodic activity going on along those additional lines, which is why they look so jagged in the contour plot. This is also why a very general utility like EZPLOT was displaying a break in the lines there, since it really isn't designed to handle specific cases of complicated and poorly behaved functions.
EDIT: (response to comments)
These additional lines may not be true zero crossings, although it is difficult to tell from the SURF plot. There may be a discontinuity at those lines, where the function shoots off to -Inf on one side of the line and Inf on the other side of the line. When rendering the surface or computing the contour, these points on either side of the line may be mistakenly connected, giving the false appearance of a zero crossing along the line.
If you want to find a zero crossing given a value of lambda, you can try using the function FZERO along with an anonymous function to turn your function of two variables f1 into a function of one variable fcn:
lambda_zero = 1.5; %# The value of lambda at the zero crossing
fcn = #(x) f1(lambda_zero,x); %# A function of one variable (lambda is fixed)
betab_zero = fzero(fcn,0.94); %# Find the value of betab at the zero crossing,
%# using 0.94 as an initial guess