I'd like to calculate the sum of a columns in a Matrix in Matlab and assign the value to another Matrix without a for loop (as I will be needed to do lots of these with little variations in the sum formula and writing for-loops for each of these would be silly).
Here is what I have so far:
finalmatrix= [
symsum((sample1Prime(i)-sample1(i))^2, i, 1, 10);
]
Note this would be one index of the final matrix.
I keep getting an error saying symsum is invalid for arguments of type double.. And a quick Google search tells me that it cannot be used for non-symbolic expressions. But no further solutions are given that meet my requirements.
Essentially what I'm trying to calculate is:
The sum from i = 1 to 10 of sample1Prime(i)-sample1(i))^2 where sample1Prime and sample1 are 10x1 Matrices.
Anyone have any ideas?
Thanks.
If you need the cumulative sum:
cumsum(sample1Prime-sample1.^2)
If you only need the final sum:
sum(sample1Prime-sample1.^2)
Related
this is a very basic problem but I didn't find any hints on it. Let's say I have a 2x4 matrix and I want to reduce the dimension of the matrix to only these columns that are in the sum larger than 1:
A=rand(2,4)
ind = sum(A,1).>1
That gives me an indicator of the columns I want to retain. Naively one would assume that I can do that:
A[:,ind]
which doesn't work as ind is a BitArray and only for Bool Arrays this is allowed, i.e., the following works
A[:,[true,true,false,true]]
in return, the following does work:
A[A.>0.5]
But it returns a vector of filtered elements.
What is the logic behind this and how do I solve my problem?
As noted in the comments, this is fixed by using a version of Julia which is >=v0.4.
I need to generate m unique random numbers in range 1 to n. Currently what I have implemented is:
round(rand(1,m)*(n-1)+1)
However, some numbers are repeated in the array. How can I get only unique numbers?
You can use randperm.
From the description:
p = randperm(n,k) returns a row vector containing k unique integers
selected randomly from 1 to n inclusive.
Thus, randperm(6,3)
might be the vector
[4 2 5]
Update
The two argument version of randperm only appeared in R2011b, so if you are using an earlier version of MATLAB then you will see that error. In this case, use:
A = randperm(n);
A = A(1:m);
As pointed out above, in Matlab versions older than R2011b randperm only accepts one input argument. In that case the easiest approach, assuming you have the Statistics Toolbx, is to use randsample:
randsample(n,m)
The randperm approach described by #Stewie appears to be the way to go in most cases. However if you can only use Matlab with 1 input argument and n is really large, it may not be feasible to use randperm on all numbers and select the first few. In this case here is what you can do:
Generate an integer between 1 and n
Generate an integer between 1 and n-1, this is the choice out of the available integers.
Repeat until you have m numbers
This can be done with randi and could even be vectorized by just drawing a lot of random numbers at each step until the unique amount is correct.
Use Shuffle, from the MATLAB File Exchange.
Index = Shuffle(n, 'index', m);
This can be done by sorting a random vector of floats:
[i,i]=sort(rand(1,range));
output=i(1:m);
i have two matrices
r=10,000x2
q=10,000x2
i have to find out those rows of q which are one value or both values(as it is a two column matrix) different then r and allocate them in another matrix, right now i am trying this.i cannot use isequal because i want to know those rows
which are not equal this code gives me the individual elements not the complete rows different
can anyone help please
if r(:,:)~=q(:,:)
IN= find(registeredPts(:,:)~=q(:,:))
end
You can probably do this using ismember. Is this what you want? Here you get the values from q in rows that are different from r.
q=[1,2;3,4;5,6]
r=[1,2;3,5;5,6]
x = q(sum(ismember(q,r),2) < 2,:)
x =
3 4
What this do:
ismember creates an array with 1's in the positions where q == r, and 0 in the remaining positions. sum(.., 2) takes the column sum of each of these rows. If the sum is less than 2, that row is included in the new array.
Update
If the values might differ some due to floating point arithmetic, check out ismemberf from the file exchange. I haven't tested it myself, but it looks good.
I need to convert this to Matlab code, and am struggling without the "table" function.
Table[{i,1000,ability,savingsrate,0,RandomInteger[{15,30}],1,0},{i,nrhhs}];
So basically, these values are all just numbers, and I think I need to use a function handle, or maybe a for loop. I'm no expert, so I really need some help?
I'm not an expert in Mathematics (just used it long time ago). According to this documentation for Table function, you are using this form:
Table[expr, {i, imax}]
generates a list of the values of expr when i runs from 1 to imax.
It looks like your statement will produce list duplicating the list in first argument increasing i from 1 to nrhhs and using different random number.
In MATLAB the output can be equivalent to a matrix or a cell array.
To create a matrix with rows as your lists you can do:
result = [ (1:nrhhs)', repmat([1000,ability,savingsrate,0],nrhhs,1), ...
randi([15 30],nrhhs,1), repmat([1,0],nrhhs,1) ];
You can convert the above matrix to a cell array:
resultcell = cell2mat(result, ones(nrhhs,1));
The "Table" example you gave creates a list of nrhhs sub-lists, each of which contains 8 numbers (i, 1000, ability, savingsrate, 0, a random integer between 15 and 30 inclusive, 1, and 0). This is essentially (though not exactly) the same as an nrhhs x 8 matrix.
Assuming you do just want a matrix out, though, an analogous for loop in Matlab would be:
result = zeros(nrhhs,8); % preallocate memory for the result
for i = 1:nrhhs
result(i,:) = [i 1000 ability savingsrate 0 randi([15 30]) 1 0];
end
This method is likely slower than yuk's answer (which makes much more efficient use of vectors to avoid the for loop), but might be a little easier to pick apart depending on how familiar you are with Matlab.
I just started matlab and need to finish this program really fast, so I don't have time to go through all the tutorials.
can someone familiar with it please explain what the following statement is doing.
[Y,I]=max(AS,[],2);
The [] between AS and 2 is what's mostly confusing me. And is the max value getting assigned to both Y and I ?
According to the reference manual,
C = max(A,[],dim) returns the largest elements along the dimension of A specified by scalar dim. For example, max(A,[],1) produces the maximum values along the first dimension (the rows) of A.
[C,I] = max(...) finds the indices of the maximum values of A, and returns them in output vector I. If there are several identical maximum values, the index of the first one found is returned.
I think [] is there just to distinguish itself from max(A,B).
C = max(A,[],dim) returns the largest elements along the dimension of A specified by scalar dim. For example, max(A,[],1) produces the maximum values along the first dimension (the rows) of A.
Also, the [C, I] = max(...) form gives you the maximum values in C, and their indices (i.e. locations) in I.
Why don't you try an example, like this? Type it into MATLAB and see what you get. It should make things much easier to see.
m = [[1;6;2] [5;8;0] [9;3;5]]
max(m,[],2)
AS is matrix.
This will return the largest elements of AS in its 2nd dimension (i.e. its columns)
This function is taking AS and producing the maximum value along the second dimension of AS. It returns the max value 'Y' and the index of it 'I'.
note the apparent wrinkle in the matlab convention; there are a number of builtin functions which have signature like:
xs = sum(x,dim)
which works 'along' the dimension dim. max and min are the oddbal exceptions:
xm = max(x,dim); %this is probably a silent semantical error!
xm = max(x,[],dim); %this is probably what you want
I sometimes wish matlab had a binary max and a collapsing max, instead of shoving them into the same function...