variable-assignment

I have a 4-D matrix A of size NxNxPxQ . How can I easily change the diagonal values to 1 for each NxN 2-D submatrix in a vectorized way? Incorporating gnovice's suggestion, an easy way to index the elements is: [N,~,P,Q]=size(A);%# get dimensions of your matrix diagIndex=repmat(logical(eye(N)),[1 1 P Q]);%# get logical indices of the diagonals A(diagIndex)=1;%# now index your matrix and set the diagonals to 1. You can actually do this very simply by directly computing the linear indices for every diagonal element, then setting them to 1: [N,N,P,Q] = size(A); diagIndex = cumsum([1:(N+1):N^2; N

I have two pieces of code. One works, another doesn't, but both seem to do identical things. This works: short s=7; but the below code doesn't. Instead, it gives error: can't assign int to short I know an integer number literal by default is int , but if it can be assigned directly above, then why not when passing to a method? class Demo1{ public static void main(String[] args){ new Demo1().go(7); } void go(short s){System.out.println("short");} } The rules are different for assignment and for method overload resolution : For assignment the JLS says : In addition, if the expression is a

i have a question about matrix assignment. say i have three matrices A, B and C, and i want to assign the elements of matrix C to the elements of A and B according to the rule C[i,j] = A[i,j] if abs(C[i,j] - A[i,j]) < abs(C[i,j] - B[i,j]) C[i,j] = B[i,j] if abs(C[i,j] - A[i,j]) > abs(C[i,j] - B[i,j]) C[i,j] = 0 if abs(C[i,j] - A[i,j]) == abs(C[i,j] - B[i,j]) how can i write it without for loops? thanks very much for your help. I think Dan Becker has the right idea, but re-computing abs(C-B) and abs(C-A) implies that the updated matrices are compared, not the original ones. I don't think this

What is the difference in these two statements in python? var = foo.bar and var = [foo.bar] I think it is making var into a list containing foo.bar but I am unsure. Also if this is the behavior and foo.bar is already a list what do you get in each case? For example: if foo.bar = [1, 2] would I get this? var = foo.bar #[1, 2] and var = [foo.bar] #[[1,2]] where [1,2] is the first element in a multidimensional list [] is an empty list. [foo.bar] is creating a new list ( [] ) with foo.bar as the first item in the list, which can then be referenced by its index: var = [foo.bar] var[0] == foo.bar #

As a small exercise before i start playing with numeric code in python I am trying to make an LDLT algorithm. Just to "get the feet wet". However I seem to be lacking a fundamental understanding of the numpy array. See the following example: def ldlt(Matrix): import numpy (NRow, NCol) = Matrix.shape for col in range(NCol): Tmp = 1/Matrix[col,col] for D in range(col+1, NCol): Matrix[col,D] = Matrix[D,col]*Tmp if __name__ == '__main__': import numpy A = numpy.array([[2,-1,0],[-1,2,-1],[0,-1,2]]) ldlt(A) The example is not the full code I am working on. However, try and run it, and set a break

error: invalid conversion from 'int' to 'int*' int *q = 8; Works fine. *q = 6; Why can't I directly assign an int to an int pointer like this: int *q = 6 ; and I can assign it safely in the next line? Because they're different things at all. The 1st one is definition of variable with initializer expression, i.e an initialization (of the pointer itself): int * q = 8; ~~~~~ ~ ~~~ type is int*; name of variable is q; initialized with 8 The 2nd one is assignment (of the object pointed by the pointer): *q = 6; ~~ ~~~ dereference on q via operator*; assign the resulting lvalue pointed by q to 6 And,

This code is provided as an example in for use with devise and OmniAuth, it works in my project . class User < ActiveRecord::Base def self.new_with_session(params, session) super.tap do |user| if data = session["devise.facebook_data"] && session["devise.facebook_data"]["extra"]["raw_info"] user.email = data["email"] if user.email.blank? end end end end I don't know why it's a single equals sign as apposed to a double equals sign, which I thought was necessary for if -statements. My IDE "intelliJ IDEA" agrees with my concerns. The only necessary thing for an if statement to be valid is a