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Questions on the manipulation of matrices in Mathematica.
1
vote
Accepted
making elements of matrix into integers
We define your matrix:
matrix = {{-1., -1., -1., -1., -1., 0., 0., 0., 0., 0., 0., 0., 0.,
0., 0., 0., 0., 0., 0., 0.}, {1., 0., 0., 0.,
0., -1., -1., -1., -1., 0., 0., 0., 0., 0., 0., 0., 0. … }, {0., 0., 0., 1., 0., 0., 0., 0., 0., 0.,
0., 1., 0., 0., 0., 0., 1., 1., 0., -1.}, {0., 0., 0., 0., 1., 0.,
0., 0., 1., 0., 0., 0., 0., 0., 1., 0., 0., 0., 1., 1.}};
and then we perform
matrix …
5
votes
How to fill lower trianglar matrix with elements of a vector
Though there are already excellent answers by Michael and cvgmt, we still have a long way to go to ten ways of achieving the result.
Borrowing from Mr.Wizard's answer here
MatrixForm@PadRight@partitio …
3
votes
Accepted
How to construct a custom-made matrix conditional on a set of rules?
So, the question essentially boils down to the following two tasks:
How do I delete all negative elements of a matrix?
How do I delete all positive elements of a matrix? … How do I delete all negative elements of a matrix?
You have the following options
bobhanlon = Clip[m0, {0, Infinity}];
jdp = (m0 /. _?(# < 0 &) :> 0);
bmf01 = m0 /. _? …
2
votes
How to repeat a matrix on it's side?
Since @kglr already used KroneckerProduct, I am demonstrating a solution that uses TensorProduct + **ArrayFlatten**
🎊 = ArrayFlatten@TensorProduct[{ConstantArray[1, #2]}, #] &;
and then
🎊[mat, 3]
…
2
votes
Remove columns basing on binary sequence
Explanation:
Rename all elements equal to 0 in the original list to something, say x
Multiply each sublist by the mask
Keep only the elements that are not equal to 0
Rename x to 0 which are the ones f …
3
votes
Prepend 0 to sublists
It's a bit strange for me that no answer used Riffle
With
list = RandomInteger[{1, 9}, {4, 5}];
zero = 0~ConstantArray~{Length@list};
we do:
ArrayReshape[
Riffle[zero,
list], {(Dimensions@list)[[ …
2
votes
Identify the positions of a marker in sublists
Since @kglr suggested, already, the use of SparseArray here's another way to go about it
Flatten /@
GatherBy[SparseArray[#]["NonzeroPositions"] & /@ ZeroCrossings,
First]
{{3, 9}, {4, 5, 8, 12, …
2
votes
Proving (or refuting) TU (totally unimodularity) of a matrix nxm
, 0}};
Dimensions@matrix
MatrixForm@matrix
{7, 7}
For the reader's convenience, the task at hand is to compute the determinant of the initial/seed matrix and all submatrices. … For the seed $7 \times 7$ matrix we run
obo = Minors[matrix, 1, Identity];
tbt = Minors[matrix, 2, Identity];
ttbtt = Minors[matrix, 3, Identity];
fbf = Minors[matrix, 4, Identity];
ffbff = Minors[matrix …
4
votes
Jacobian matrix evaluation at a point
VectorQ, x_List] :=
Det[JacobianMatrix[f, x]] /; Equal @@ (Dimensions /@ {f, x})
The Jacobian matrix is
JacobianMatrix[{f1[x, y], f2[x, y]}, {x, y}]
and you can evaluate at a point using either …
6
votes
How do I flatten a matrix of lists while maintaining the structure of the list?
We grab the matrix from the OP
matrix = {{{a, b, c}, {e, f, g}}, {{h, i, j}, {k, l, m}}}
0. … Using Sum
The code is
Sum[matrix[[xx1, xx2]], {xx1, 1, (Dimensions@matrix)[[1]]}, {xx2,
1, (Dimensions@matrix)[[2]]}]
The above is an automated approach of the following
matrix[[1, 1]] + matrix[[1, …
3
votes
Determine value of parameters in a matrix such that it is unitary
Expanding my comment:
U = {{x1, -x2, x3}, {-x1, 0, x3}, {x1, x2, 0}};
U // MatrixForm
The other required matrices
Inverse[U] // MatrixForm
Transpose[U] // MatrixForm
I am hoping that now it …
3
votes
Create Matrix where its entries come from functions
Another possibility
n = 5;
first = Table[i^2, {i, n}];
rest = Table[2 i j, {i, n}, {j, 2, n}];
MatrixForm@ArrayReshape[Thread@{first, rest}, {n, n}]
7
votes
How to use ArrayFlatten
@Nasser gave the canonical answer and this is more of a general comment, hopefully useful.
Instead of using ArrayFlatten you can consider ArrayReshape
That is
x = ConstantArray[0, 4];
x = Thread@{x};
…
1
vote
Getting zero for special positions in a matrix
I think that's the simplest way
list = {{1, 2, 3, 2, 3}, {3, 1, 1, 2, 3}, {3, 2, 1, 3, 2}, {1, 2, 1,
1, 1}};
list /. {a_, b_, c_, d_, e_} :> {a, 0, 0, d, 0}
3
votes
Delete zero rows in a matrix
I am adding some contributions. As far as I checked there's no overlap with the suggestions so far. If someone spots something, I would appreciate a comment and I will remove the duplicate.
I am grabb …