=======================
===== arrays ==========
=======================


### Example 1 

----- given vector:  ------

v = [ 2 4 -3 0 5 0 -1 -1 1]

-- the sum of the elements of the vector

s = sum(v)

-- maximum, minimum ---

mx = max(v); mn = min(v);

-- number of negative numbers ---

zv = (v<0)    % ones on places of negative numbers, zeros otherwise
z = sum(zv)   

-- number of nonzero numbers ---

n = sum(v~=0)

-- indices of nonzero numbers ---

nv = find(v)    % indices of nonzero numbers
n = length(nv)  % their number

-- indices of negative numbers

zv = find(v<0)

-- finding all the negative numbers in v ---

zv = find(v<0)
zap = v(zv)

-- setting all negative numbers in v to zeros ---

zv = find(v<0)
v(zv) = 0

-- appending one more element after the last one ---
y(end+1) = -5

-- deleting the first element from the vector ---
y(1) = []  


================================



### Example 2 

----- given array (matrix):  ------

A = [ 2   3   0  -1
      0  -2   1   3 ]

-- sums of columns, rows, sum of all elements ---

ss = sum(A); sr = sum(A,2); s = sum(sum(A)); 

-- maxima for columns, rows, over all elements (analog. minimum) ---

mxs = max(A); mxr = max(A')'; mx = max(max(A));

-- numbers of negative numbers in columns and over all elements ---

zA = (A<0)        % ones on the places of negative numbers
zs = sum(zA); z = sum(sum(zA))

-- number of nonzero numbers ---

n = sum(sum(A~=0))

-- number of nonzero numbers in the second row ---

n = sum(A(2,:)~=0)

-- indices of nonzero numbers

iA = find(A)    % indices of nonzero numbers (ordered by columns)
[ir, is] = find(A)  % indices of rows and columns with nonzero numbers

-- indices of negative numbers

zA = find(A<0)

-- finding all negative numbers in A

zA = find(A<0)
zap = A(zA)

-- setting all negative numbers in A to zeros

zA = find(A<0)
A(zA) = 0

================================


### Example 3 

----- given square matrix:  ------

A = [ 3 5 -1; 1 -4 2; 0 -1 1]

----- decompose it to the sum A = L + D + U, where   ---
----- D - diagonal, L - lower triang., U - upper tr. ---

D = diag(diag(A))
L = tril(A,-1)
U = triu(A,1)

==================================