I'm struggling with a plot I want to make using a for-loop.
I know it works when I add it after the loop (just a simple plot). But I want to try it in this other way.
fib = ones(1:10);
for k=3:10
hold on
fib(k) = fib(k-1) + fib(k-2);
plot(k,fib(k))
end
hold off
The output is a plot, but there are no points visible.
You need to specify a marker. The documentation says:
If one of X or Y is a scalar and the other is either a scalar or a vector, then the plot function plots discrete points. However, to see the points you must specify a marker symbol, for example, plot(X,Y,'o')
So it will be:
plot(k,fib(k),'o');
Also note that you're creating a 10-dimensional array with fib = ones(1:10);. You most probably meant to write a comma instead of colon in between 1 and 10 to create a row vector. i.e.
fib = ones(1,10);
or a column vector as HansHirse suggested:
fib = ones(10,1);
Related
I am trying to understand these by myself
,
I want to simulate some straight lines, in Matlab, as follows:
f(t,z)=a(z)t+b(z) where a(z) and b(z) are uniformly distributed random variable in the interval [-1,1] and t is time between [-2,2]. More simply: f(t)= at+b, and z is the random index of the constant (a,b) and let say [-1,+1] is the sample space for z and z is uniformly distributed.
Could anyone help me with the code? Is there any way to show the random generation of the straight line as an animation? Thank you very much for any help.
I am trying like this:
a= rand(-1,1);
b=rand(-1,1);
-2<t<2;
f=a*t+b;
plot(t, f);
But I am getting error Unrecognized function or variable 't'.
Your attempt is not valid MATLAB syntax,
-2<t<2 does not do anything, other than produce the error you're seeing because t does not exist
f = a*t+b you can't define functions like this, you probably want to use an anonymous function.
You can't plot t because you haven't defined it, and you can't plot f because you haven't properly defined that either in terms of a valid t.
You need to define some discrete values for t. In this case two values is enough, because you're only plotting straight lines anyway. You could use linspace or the colon operator to create a finer spaced array for whatever reason.
N = 10; % Number of lines to plot
t = [-2,2]; % We want lines between -2 and 2
a = rand(N,1)*2-1; % N random values between -1 and +1
b = rand(N,1)*2-1; % N random values between -1 and +1
f = #(t,z) a(z)*t + b(z); % Define f in terms of axis t and index z
% Plotting
figure; hold on;
for iz = 1:N
plot( t, f(t,iz) );
end
This gives an image something like this:
If you need an "animation", you could add a pause, e.g. pause(1) inside the loop
I have a matlab indexing question. I have a vector of 34 elements that I would like to plot in a for loop. However, I do not wish to plot them all at once. It would be great if I were able to plot elements 1:6, then 7:11, then 12:20, and so on. Is it possible to do this type of plotting in a for loop? If it is, I am having trouble with the indexing. Since these elements are all in sequential order, matlab seems to want to plot them all together. Any help would be appreciated. Thanks!
Here is an example of what I am trying to do:
for i = 1: [1:6, 7:11, 12:20]
plot(x(i), y(i))
end
Hopefully, I can get three plot, one with data from elements 1:6, another from elements 7:11, and the last one from elements 12:20.
You can just use a cell to store the variable-length vectors containing the various indices:
x = linspace(0, 1, 20);
y = x;
i_cell = {1:6, 7:11, 12:20};
for i = 1:length(i_cell)
figure
indices = i_cell{i}
plot(x(indices), y(indices))
end
Im just trying to draw a line through the following points in matlab. Currently the line extends only to the points. I need to to extend and intercept the x axis. The code is below
A = [209.45 198.066 162.759];
B = [1.805 1.637 1.115];
plot(A,B,'*');
axis([0 210 0 2]);
hold on
line(A,B)
hold off
If you want to augment your points with a corresponding y==0 point, I suggest using interp1 to obtain the x-intercept:
A = [209.45 198.066 162.759];
B = [1.805 1.637 1.115];
x0 = interp1(B,A,0,'linear','extrap'); %extrapolate (y,x) at y==0 to get x0
[newA, inds] = sort([x0 A]); %insert x0 where it belongs
newB = [0 B];
newB = newB(inds); %keep the same order with B
plot(A,B,'b*',newA,newB,'b-');
This will use interp1 to perform a linear interpolant, with extrapolation switched on. By interpolating (B,A) pairs, we in effect invert your linear function.
Next we add the (x0,0) point to the data, but since matlab draws lines in the order of the points, we have to sort the vector according to x component. The sorting order is then used to keep the same order in the extended B vector.
Finally the line is plotted. I made use of plot with a linespec of '-' to draw the line in the same command as the points themselves. If it doesn't bother you that the (x0,0) point is also indicated, you can plot both markers and lines together using plot(newA,newB,'*-'); which ensures that the colors match up (in the above code I manually set the same blue colour on both plots).
I am having trouble figuring out how display 4 variables in my plot.
I want to vary the independent variables X,V, to produce the dependent variables Y and Z.
Y is a function of X AND V. And Z is a function of Y AND X.
This may be easier to see the dependencies: X, V, Y(X,V), Z(X,Y(X,V)).
I have used the surf function to plot X,Y,Z, but I also want to know the values of V, which I cannot currently ascertain.
Here is some test data to illustrate:
X = linspace(1,5,5)
V = linspace(1,5,5)
Capture = []
for j = 1:length(V)
Y = X.*V(j)
Capture = [Capture;Y]
end
[X,V] = meshgrid(X,V);
Z = Capture.*X
surf(X,Y,Z)
If I use the data cursor, I can see values of X,Y,Z, but I would also like to know the values of V. I know that the way I have it set up is correct because if I make two plots, say:
surf(X,Y,Z)
surf(X,V,Z)
and then use the data cursor to go on the same point of X and Z for both graphs the values for V and Y are what they should be for that point (X,Z).
Is there anyway to show the values for X,Y,V and Z without having to generate two separate graphs?
Thanks!
Using color as your 4th dimension is a possibility (whether it looks good to you is a matter of taste).
surf(X,Y,Z,V); #% 4th arg (V) is mapped onto the current colormap
You can change the colormap to suit your tastes.
colorbar #% displays a colorbar legend showing the value-color mapping
Edit: The questioner wants to see exactly the data in the not-shown array, rather than just a color. This is a job for custom data cursor function. Below I've implemented this using purely anonymous functions; doing it within a function file would be slightly more straightforward.
#% Step 0: create a function to index into an array...
#% returned by 'get' all in one step
#% The find(ismember... bit is so it returns an empty matrix...
#% if the index is out of bounds (if/else statements don't work...
#% in anonymous functions)
getel = #(x,i) x(find(ismember(1:numel(x),i)));
#% Step 1: create a custom data cursor function that takes...
#% the additional matrix as a parameter
myfunc = #(obj,event_obj,data) {...
['X: ' num2str(getel(get(event_obj,'position'),1))],...
['Y: ' num2str(getel(get(event_obj,'position'),2))],...
['Z: ' num2str(getel(get(event_obj,'position'),3))],...
['V: ' num2str(getel(data,get(event_obj,'dataindex')))] };
#% Step 2: get a handle to the datacursormode object for the figure
dcm_obj = datacursormode(gcf);
#% Step 3: enable the object
set(dcm_obj,'enable','on')
#% Step 4: set the custom function as the updatefcn, and give it the extra...
#% data to be displayed
set(dcm_obj,'UpdateFcn',{myfunc,V})
Now the tooltip should display the extra data. Note that if you change the data in the plot, you'll need to repeat Step 4 to pass the new data into the function.
I would like to write a program which plots the points on top of a semicircle on a certain interval and a straight line everywhere else. Something like this: __n__.
I defined a time domain, which was stored as a vector (t = 0:0.01:5). I assumed that I could define the points on the top of the semicircle using elements of the time vector:
if t>=2|t<=2.3
y = sqrt(.15^2-(t-2.15)^2);
but MATLAB produced an error message saying only square matrices can be squared.
I tried to utilize indices to show that I wanted to square an element of the t vector and not the whole vector:
i = [200:230];
for t(200:230)
y = sqrt(.15^2-(t(i)-2.15)^2);
After these failures, I noticed that squaring a square matrix with one column of non-zero elements would produce a new square matrix with a column of the first matrix's elements squared. If there is some way to eliminate the extra columns of zeros after squaring the matrix, I could use that property of matrices to square the values of the t vector.
What is the simplest and most effective way to address this problem?
It sounds like you want to draw a horizontal line with a semicircular "bump" on it. Here's how you can do this:
t = 0:0.01:5; % Create the time vector
y = zeros(size(t)); % Create a zero vector the same size as t
index = find((t >= 2) & (t <= 2.3)); % Find a set of indices into t
y(index) = sqrt(.15^2-(t(index)-2.15).^2); % Add the "bump" to y
y(1:index(1)) = y(index(1)); % Add the line before the "bump"
y(index(end):end) = y(index(end)); % Add the line after the "bump"
In the above solution, the lines before and after the "bump" could be slightly higher or lower than one another (depending on where your samples in t fall). If you want to make sure they are at the same height, you can instead do the following:
index = (t >= 2) & (t <= 2.3); % Find a set of logical indices
y(index) = sqrt(.15^2-(t(index)-2.15).^2); % Add the "bump" to y
% OPTION #1:
y(~index) = y(find(index,1,'first')); % Use the first circle point as the height
% OPTION #2:
y(~index) = y(find(index,1,'last')); % Use the last circle point as the height
Finally, you can plot the line:
plot(t,y);
Hold on, so your question is, you want to square each element of a vector? All you have to do is:
t.^2
The . represents an element-wise operation in MATLAB on a vector or an array.
And secondly, if I understood your problem currently, you want to create a vector y, which contains a function of elements of t such that t>=2 | t <=2.3?
If so, all you have to do is this:
y = sqrt(0.15^2-(t( (t>=2|t<=2.3) )-2.15).^2));
Essentially, I created a logical index (t>=2 | t<=2.3) and used to access only those elements (which I wanted) in t.
Also, I didn't fully understand what you wanted to achieve. Do you want to plot the topmost point (maxima) of a semicircular curve?