I have a function M file defined as follows:
function [v,m ] = myfun(y)
m=mean(y);
v=var(y);
end
For a given vector which consists of integers from 1 to 100 for simplicity, I want to do bootstrap for 10 times and obtain both mean and variance for each bootstrapped sample. The following wouldn't work:
y=[1:100]';
[m,v]=bootstrp(10,#(x) myfun(x),y);
Could any one help me out of here? Thanks in advance!
Why don't you think it works? This does exactly what you're specifying. However, I would do away with specifying a separate function and putting the mean and standard deviation directly in the anonymous function itself. Specifically:
stats = bootstrp(10, #(x) [mean(x) var(x)], y);
In this case, you will get a 10 x 2 matrix. The first column will give you the mean of each boostrapped sample while the next column will give you the variance of each bootstrapped sample. Specifically, the first row gives you the mean (first column) and variance (second column) of the first sample. The second row gives you the mean and variance of the second sample, and so on. Each column of your output in stats will give you whatever measure you are calculating in the corresponding position in the output vector of your function.
Check the documentation for bootstrp here: http://www.mathworks.com/help/stats/bootstrp.html
To answer your question as to why you're getting the too many outputs error is because you need to output only one variable, but you are outputting two. As such, group your variables into a single vector like so:
function [out] = myfun(y)
m=mean(y);
v=var(y);
out = [m,v];
end
If you now run your bootstrp code with this function, it should now work.
Related
I have a matrix (type:double) of size 106 x 103. The matrix represents European gridded temperature data for one timestep (a day).
For every day, I want to calculate the degree days (thermal time) for a species, based on the temperature recorded for each 'cell' (i,j element) in the matrix using a formula that I have coded in Matlab based on a sinewave approach.
So, ultimately, what I want to do is being able to apply a calculation to my matrix, that will provide individual output for each grid cell (i,j element) dependent on the temperature data that is recorded there.
I could do this with a loop, but I have to accumulate these degree days for multiple years, so I would prefer to find a way of applying the calculation to each element in a daily matrix simultaneously (and then looping through the days (matrices)).
From what I have read, you can use a cellfun if your matrix is a cell array (mine is not).
Then I was also looking at the bsxfun option, but it seems like the functions are just standard functions..like mean, max etc.
So now, I'm looking at using arrayfun in conjunction with a function I create from my algorithm to calculate degree days.
I have been trying to write a test function but Matlab keeps throwing up the same error:
I type:
function output=degreedays(x)
and Matlab throws back:
Error: Function definitions are not permitted in this context.
Can someone tell me what I'm doing wrong? Why is it not accepting the declaration of the function name?
MATLAB does not allow you to define named functions like this at the command line. You need to place your function definition in a file. MATLAB then can call that function by the name of the file - so in your case, put your function definition in a file called degreedays.m.
See the doc for more: https://uk.mathworks.com/help/matlab/matlab_prog/create-functions-in-files.html .
I am training an ANN, and I want to have different instances of training. In each instance, I want to find the maximum difference between the actual and predicted output. Then I want to take the average of all these maximums.
My code so far is:
maximum = [];
k=1;
for k = 1:5
%Train network
layers = [ ...
imageInputLayer([250 1 1])
reluLayer
fullyConnectedLayer(100)
fullyConnectedLayer(100)
fullyConnectedLayer(1)
regressionLayer];
options = trainingOptions('sgdm','InitialLearnRate',0.1, ...
'MaxEpochs',1000);
net = trainNetwork(nnntrain,nnnfluidtrain,layers,options);
net.Layers
%Test network
predictedn = predict(net,nnntest);
maximum = append(maximum, max(abs(predictedn-nnnfluidtest)));
k=k+1
end
My intent is to produce a list named 'maximum' with five elements (the max of each ANN training instance) that I would then like to take the average of.
However, it keeps giving me the error:
wrong number of input arguments for obsolete matrix-based syntax
when it tries to append. The first input is a list while the second is a 1x1 single.
Appending in MATLAB is a native operation. You append elements by actually building a new vector where the original vector is part of the input.
Therefore:
maximum = [maximum max(abs(predictedn-nnnfluidtest))];
If for some reason you would like to do it in function form, the function you are looking for is cat which is short form for concatenate. The append function is seen in multiple toolboxes but each one of them does not do what you want. cat is what you want but you still need to provide the original input vector as part of the arguments:
maximum = cat(2, maximum, max(abs(predictedn-nnnfluidtest)));
The first argument is the axis you want to append to. To respect the code that you're doing above, you want the columns to increase as you extend your vector so that is the second axis, or the axis being 2.
Hi, I am trying to write a function as per the question. I have tried to create four sub-matrices which are the reverse of each other and then multiply to give the products demanded by the question. My attempt:
function T = custom_blocksT(n,m)
T(1:end,end-1:1);
T(1:end,end:-1:1)*2;
T(1:end,end:-1:1)*3;
T(1:end,end:-1:1)*4;
What I'm unsure of is
(i) What do the the indivual sub-matrices(T(1:end,end-1:1);)need to be equal to? I was thinking of(1:3)?
(ii) I tried to create a generic sub-matrix which can take any size matrix input using end was this correct or can't you do that? I keep getting this error
Undefined function or variable 'T'.
Error in custom_blocksT (line 2)
T(1:end,end-1:1);
I have searched the Matlab documentation and stacked overflow, but the problem is I'm not quite sure what I'm supposed to be looking for in terms of solving this question.
If someone could help me I would be very thankfull.
There are many problems with your function:
function T = custom_blocksT(n,m)
T(1:end,end-1:1);
T(1:end,end:-1:1)*2;
T(1:end,end:-1:1)*3;
T(1:end,end:-1:1)*4;
end
This is an extremely basic question, I highly recommend you find and work through some very basic MATLAB tutorials before continuing, even before reading this answer to be honest.
That said here is what you should have done and a bit of what you did wrong:
First, you are getting the error that T dos not exist because it doesn't. The only variables that exist in your function are those that you create in the function or those that are passed in as parameters. You should have passed in T as a parameter, but instead you passed in n and m which you don't use.
In the question, they call the function using the example:
custom_blocks([1:3;3:-1:1])
So you can see that they are only passing in one variable, your function takes two and that's already a problem. The one variable is the matrix, not it's dimensions. And the matrix they are passing in is [1:3;3:-1:1] which if you type in the command line you will see gives you
[1 2 3
3 2 1]
So for your first line to take in one argument which is that matrix it should rather read
function TOut = custom_blocks(TIn)
Now what they are asking you to do is create a matrix, TOut, which is just different multiples of TIn concatenated.
What you've done with say TIn(1:end,end-1:1)*2; is just ask MATLAB to multiple TIn by 2 (that's the only correct bit) but then do nothing with it. Furthermore, indexing the rows by 1:end will do what you want (i.e. request all the rows) but in MATLAB you can actually just use : for that. Indexing the columns by end-1:1 will also call all the columns, but in reverse order. So in effect you are flipping your matrix left-to-right which I'm sure is not what you wanted. So you could have just written TIn(:,:) but since that's just requesting the entire matrix unchanged you could actually just write TIn.
So now to multiply and concatenate (i.e. stick together) you do this
TOut = [TIn, TIn*2; TIn*3, TIn*4]
The [] is like a concatenate operation where , is for horizontal and ; is for vertical concatenation.
Putting it all together:
function TOut = custom_blocks(TIn)
TOut = [TIn, TIn*2; TIn*3, TIn*4];
end
I'm interested in understanding the variety of zeroes that a given function produces with the ultimate goal of identifying the what frequencies are passed in high/low pass filters. My idea is that finding the lowest value zero of a filter will identify the passband for a LPF specifically. I'm attempting to use the [hz,hp,ht] = zplane(z,p) function to do so.
The description for that function reads "returns vectors of handles to the zero lines, hz". Could someone help me with what a vector of a handle is and what I do with one to be able to find the various zeros?
For example, a simple 5-point running average filter:
runavh = (1/5) * ones(1,5);
using zplane(runavh) gives an acceptable pole/zero plot, but running the [hz,hp,ht] = zplane(z,p) function results in hz=175.1075. I don't know what this number represents and how to use it.
Many thanks.
Using the get command, you can find out things about the data.
For example, type G=get(hz) to get a list of properties of the zero lines. Then the XData is given by G.XData, i.e. X=G.XData.
Alternatively, you can only pull out the data you want
X=get(hz,'XData')
Hope that helps.
i have two problems in mathematica and want to do them in matlab:
measure := RandomReal[] - 0.5
m = 10000;
data = Table[measure, {m}];
fig1 = ListPlot[data, PlotStyle -> {PointSize[0.015]}]
Histogram[data]
matlab:
measure =# (m) rand(1,m)-0.5
m=10000;
for i=1:m
data(:,i)=measure(:,i);
end
figure(1)
plot(data,'b.','MarkerSize',0.015)
figure(2)
hist(data)
And it gives me :
??? The following error occurred
converting from function_handle to
double: Error using ==> double
If i do :
measure =rand()-0.5
m=10000;
data=rand(1,m)-0.5
then, i get the right results in plot1 but in plot 2 the y=axis is wrong.
Also, if i have this in mathematica :
steps[m_] := Table[2 RandomInteger[] - 1, {m}]
steps[20]
Walk1D[n_] := FoldList[Plus, 0, steps[n]]
LastPoint1D[n_] := Fold[Plus, 0, steps[n]]
ListPlot[Walk1D[10^4]]
I did this :
steps = # (m) 2*randint(1,m,2)-1;
steps(20)
Walk1D =# (n) cumsum(0:steps(n)) --> this is ok i think
LastPointold1D= # (n) cumsum(0:steps(n))
LastPoint1D= # (n) LastPointold1D(end)-->but here i now i must take the last "folding"
Walk1D(10)
LastPoint1D(10000)
plot(Walk1D(10000),'b')
and i get an empty matrix and no plot..
Since #Itamar essentially answered your first question, here is a comment on the second one. You did it almost right. You need to define
Walk1D = # (n) cumsum(steps(n));
since cumsum is a direct analog of FoldList[Plus,0,your-list]. Then, the plot in your code works fine. Also, notice that, either in your Mathematica or Matlab code, it is not necessary to define LastPoint1D separately - in both cases, it is the last point of your generated list (vector) steps.
EDIT:
Expanding a bit on LastPoint1D: my guess is that you want it to be a last point of the walk computed by Walk1D. Therefore, it would IMO make sense to just make it a function of a generated walk (vector), that returns its last point. For example:
lastPoint1D = #(walk) (walk(end));
Then, you use it as:
walk = Walk1D(10000);
lastPoint1D(walk)
HTH
You have a few errors/mistakes translating your code to Matlab:
If I am not wrong, the line data = Table[measure, {m}]; creates m copies of measure, which in your case will create a random vector of size (1,m). If that is true, in Matlab it would simply be data = measure(m);
The function you define gets a single argument m, therefor it makes no sense using a matrix notation (the :) when calling it.
Just as a side-note, if you insert data into a matrix inside a for loop, it will run much faster if you allocate the matrix in advance, otherwise Matlab will re-allocate memory to resize the matrix in each iteration. You do this by data = zeros(1,m);.
What do you mean by "in plot 2 the y=axis is wrong"? What do you expect it to be?
EDIT
Regarding your 2nd question, it would be easier to help you if you describe in words what you want to achieve, rather than trying to read your (error producing) code. One thing which is clearly wrong is using expression like 0:steps(n), since you use m:n with two scalars m and n to produce a vector, but steps(n) produces a vector, not a scalar. You probably get an empty matrix since the first value in the vector returned by steps(n) might be -1, and 0:-1 produces an empty vector.