Understand a command line to create a matrix

Hi all,

I am trying to write the following matlab line into another program, I already found it in the internet, it works perfectly, but I can not understand excatly how it work ??

clc; nelments= 3;   npoint= 5;
    connect=(1:npoint) + (npoint-1)*(0:nelments-1).'

Answer 1

[Geoff Hayes]

@Mark Sc - this is an interesting piece of code. Given that

>> x = (1:npoint) 

x =
     1     2     3     4     5

and that

>> y = (npoint-1)*(0:nelments-1).'

y =
     0
     4
     8

we are trying to add a 1x5 matrix with a 3x1 matrix with the output being a 3x5. Looking at the plus for 2-D inputs, if one input is a column vector, and the other is a row vector then your output (in this case) will be that 3x5 matrix where we add 0 to each element of x to get the first row of the new matrix, 4 to each element of x to get the second row of the new matrix, and 8 to each element of x to get the third row.

>> x + y

ans =
     1     2     3     4     5
     5     6     7     8     9
     9    10    11    12    13

[Mark Sc]

@Geoff Hayes

Thank you for clear explanation,

Not sure if possible to ask could we do the same in python ??

If so, could you provide it ??

[Geoff Hayes]

@Mark Sc - I tried doing something similar in Python but observed an error

Traceback (most recent call last):
  File "py-add.py", line 4, in <module>
    c=a+b
ValueError: operands could not be broadcast together with shapes (5) (3) 

so from this one example it seems that it behaves a little differently than MATLAB. It shouldn't be too hard to write the code to do what you want though.