Ok, so the patch function lets us draw multiple polygons with e.g.
patch(X,Y,'r')
where X and Y are m-by-n matrices. This draws n polygons with m vertices.
But what if I want each of those n polygons to have a unique alpha transparency value?
patch(X,Y,'r', ??? SOME CODE TO USE A VECTOR OF ALPHA VALUES ???)
The documentation is confusing me to death. I can't use a for loop, since I need to draw many patch objects very quickly. Could somebody kindly provide a code example? Thanks everyone.
Looks like the FaceVertexAlphaData property is the key: Here is some sample code:
X = [...
1 2 3 ; ...
4 5 6 ; ...
7 8 9 ; ...
10 11 12];
Y = [...
2 5 8; ...
3 6 9; ...
1 4 7; ...
-1 3 6];
h = patch( X, Y, 'r');
set(h,'FaceAlpha','flat','FaceVertexAlphaData',[.2; .4; .8])
docsearch patch properties for more information.
Related
I have two columns with data, x and y. Now I want to connect these data points in the order they appear in the columns. Say I have x=[1 2 3 4 3 2] and y=[3 4 2 1 3 3]. Now if I use spline to create a smooth curve, it 'sorts' the columns in an increasing order. I would like it to just take the data points, thus firstly x(1),y(1) and connect these to x(2), y(2) and so on.
Is this possible?
spline generates a function from the reals to the reals. This means a more general curve cannot be expressed as y = f(x) but we need to parametrize it as (x(t), y(t)):
x=[1 2 3 4 3 2];
y=[3 4 2 1 3 3];
plot(x,y,'o-');
% cannot be represented as function y=f(x)
% because x=2 and 3 have two different y values
% -> parametrize x and y:
t = 1:numel(x);
tt = linspace(min(t), max(t), 1000);;
tx = spline(t,x,tt);
ty = spline(t,y,tt);
hold on
plot(tx,ty,'-');
Let
input = [0 0 0 5 5 7 8 8];
I now want to transform this vector into the form
output = [3 3 3 3 5 5 6 8];
Which basically is a stairs plot.
Explanation
The input vector is used to plot data points along the x-axis. The y-axis is thereby provided by 1:length(input). So the resulting plot shows the cumulative number of datapoints along the y-axis and the time of occurrence along the x-axis.
I now want to fit a model against my dataset. Therefor I need a vector that provides the correct value for a certain time (x-value).
The desired output vector basically is the result of a stairs plot. I am looking for an efficient way to generate the desired vector in matlab. The result of
[x, y] = stairs(input, 1:length(input));
did not bring me any closer.
It can be done with bsfxun as follows:
x = [0 0 0 5 5 7 8 8];
y = sum(bsxfun(#le, x(:), min(x):max(x)), 1);
This counts, for each element in 1:numel(x), how many elements of x are less than or equal to that.
I have two vectors of the same size. The first one can have any different numbers with any order, the second one is decreasing (but can have the same elements) and consists of only positive integers. For example:
a = [7 8 13 6];
b = [5 2 2 1];
I would like to plot them in the following way: on the x axis I have points from a vector and on the y axis I have the sum of elements from vector b before this points divided by the sum(b). Therefore I will have points:
(7; 0.5) - 0.5 = 5/(5+2+2+1)
(8; 0.7) - 0.7 = (5+2)/(5+2+2+1)
(13; 0.9) ...
(6; 1) ...
I assume that this explanation might not help, so I included the image
Because this looks to me as a cumulative distribution function, I tried to find luck with cdfplot but with no success.
I have another option is to draw the image by plotting each line segment separately, but I hope that there is a better way of doing this.
I find the values on the x axis a little confusing. Leaving that aside for the moment, I think this does what you want:
b = [5 2 2 1];
stairs(cumsum(b)/sum(b));
set(gca,'Ylim',[0 1])
And if you really need those values on the x axis, simply rename the ticks of that axis:
a = [7 8 13 6];
set(gca,'xtick',1:length(b),'xticklabel',a)
Also grid on will add grid to the plot
I need help solving an indexing problem. The assigned problem states: Two matrices (x and y) give the coordinates to form matrix B from matrix A. Produce the matrix B which contains the values of A at the given coordinates in x and y.
For instance:
x = [1 1 1; 2 2 1]
y = [1 2 1; 3 2 4]
%This would read as (1,1),(1,2),(1,1),(2,3),(2,2),(1,4)
% Given matrix:
A = [6 7 8 9; 10 11 12 13];
%This would give us this answer for B (using the coordinate scheme above):
B=[6 7 6; 12 11 9];
I'm guessing I need to use the find function in conjunction with a sub2ind function, but I'm not 100% sure how to translate that into working code. The only thing I can think of would be to do something like this:
B=((x(1),(y(1)), (x(2),y(2)).......
But that would only work for the defined matrix above, not a randomly generated matrix. I tried looking for a similar problem on the site, but I couldn't find one. Your help would be really appreciated!
You can't do it for randomly generated matrices, because you have to ensure that matrix A has lines and columns as required from the values of x and y.
In this case, you can write:
for i=1:length(x(:))
B(i)=A(x(i),y(i));
end
B=reshape(B,size(x));
My task is to write MATLAB code to produce a 4-part logo as shown in the screenshot. The top left should be black and the bottom right should be white. The other
two colours should be chosen randomly by the program.
I have taken the following approach:
clear all
clc
close all
x = [1 4 1 4 1 6.5 7 7];
y = [3 4 5.5 5 8 7 8 3];
fill(x,y,'k')
which creates the upper left black part. I wonder if that approach is good enough and if it is, what is the next step. I thought of storing those two variables in a shape object or something (I'm not familiar with Matlab) and rotate it somehow. Could you help me with that?
You don't need to rotate, just use the symmetry
clear all
clc
close all
x = [1 4 1 4 1 6.5 7 7];
y = [3 4 5.5 5 8 7 8 3]-3;
clrs=jet(10);
fill(x,y,'k')
hold on;
fill(2*max(x)-x,y,clrs(round(rand*10),:))
fill(x,-y,clrs(round(rand*10),:))
fill(2*max(x)-x,-y,'w')
The easiest way to do this all this, is to make sure that your center point (i.e. the point where the different colors meet), is positioned at [0,0]. Then a rotation of the figure (by multiple of 90°) boils down to changing the sign of either the x and/or y values of your contour.
If you need the figure to be at a point different from [0 0], just add these coordinates after you did the rotation.
So starting from your code, you can do this:
x = [1 4 1 4 1 6.5 7 7]-7;
y = [3 4 5.5 5 8 7 8 3]-3;
c = [5 6];
col = [0 0 0;
rand(2,3);
1 1 1];
fill( x+c(1), y+c(2),col(1,:)); hold on;
fill(-x+c(1), y+c(2),col(2,:));
fill( x+c(1),-y+c(2),col(3,:));
fill(-x+c(1),-y+c(2),col(4,:)); hold off;
edit: Clarification for the col and c variables.
The variable col contains the colors to be used in rgb style, where each row is a color. rand generates uniformly random numbers in the range [0,1], which is also where the values for the colors are expected to be. In the code above a 2x3 random matrix is generated, so that means 2 random colors which fits perfectly within the col matrix.
The variable c contains the center of your figure. If you look at the plot, the center will be at [5 6] (so 5 along the x axis and 6 along the y axis). You could use two variables instead, but I think that keeping both together in a variable is easier to deal with. I would personally do the same for your x and y variables, as that would allow you to use rotation matrices more easily, but that's just a matter of choice.