Matrices Built from Shifted Elements
03-06-2019, 01:26 PM
Post: #1
 Eddie W. Shore Senior Member Posts: 1,582 Joined: Dec 2013
Matrices Built from Shifted Elements
The programs LSM (left-shift matrix) and RSM (right-shift matrx) create a n x n matrix based on the elements of a given list. Each row has each of the elements rotated one element.

For LSM, each row has the elements shifted to the left one element.

For RSM, each row has the elements shifted to the right one element.

HP Prime Program: LSM
Code:

EXPORT LSM(L0)
BEGIN
// EWS 2019-03-02
// left shift matrix
LOCAL L1,N,M0,K;
N:=SIZE(L0);
L1:=L0;
FOR K FROM 1 TO N-1 DO
L0:=CONCAT(L0,L1);
END;
M0:=list2mat(L0,N);
RETURN M0;
END;

HP Prime Program: RSM
Code:

EXPORT RSM(L0)
BEGIN
// EWS 2019-03-03
// right shift matrix
LOCAL L1,N,M0,K;
N:=SIZE(L0);
L1:=L0;
FOR K FROM 1 TO N-1 DO
L1:=REVERSE(CONCAT(
tail(REVERSE(L1)),
));
L0:=CONCAT(L0,L1);
END;
M0:=list2mat(L0,N);
RETURN M0;
END;

Note: The program RSM creates a circulant matrix.

Example:

list = {1, 7, 8, -2, 0}

LSM({1, 7, 8, -2, 0} returns:

[ [ 1, 7, 8, -2, 0 ]
[ 7, 8, -2, 0, 1 ]
[ 8, -2, 0, 1, 7 ]
[ -2, 0, 1, 7, 8 ]
[ 0, 1, 7, 8, -2 ] ]

RSM({1,7,8,-2,0}) returns:

[ [ 1, 7, 8, -2, 0 ]
[ 0, 1, 7, 8, -2 ]
[ -2, 0, 1, 7, 8 ]
[ 8, -2, 0, 1, 7 ]
[ 7, 8, -2, 0, 1 ] ]

Blog post: https://edspi31415.blogspot.com/2019/03/...ifted.html
03-06-2019, 04:32 PM
Post: #2
 Didier Lachieze Senior Member Posts: 1,631 Joined: Dec 2013
RE: Matrices Built from Shifted Elements
Interesting topic, another way to do it would be to use MAKEMAT like this:

Code:
EXPORT LSM(L0)
BEGIN
LOCAL N:= SIZE(L0);
MAKEMAT(L0((J+I-1) MOD N),N,N);   // left shift matrix
END;

EXPORT RSM(L0)
BEGIN
LOCAL N:= SIZE(L0);
MAKEMAT(L0((J-I+1) MOD N),N,N);   // right shift matrix
END;
03-06-2019, 05:41 PM
Post: #3
 John Keith Senior Member Posts: 1,027 Joined: Dec 2013
RE: Matrices Built from Shifted Elements
Interesting, thanks for posting. As an aside, your left-shifted matrix is a Hankel matrix, useful in linear algebra and integer transforms.
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