div = divergence(X,Y,U,V) computes the divergence of a 2-D vector field U,
V. The arrays X, Y define the coordinates for U, V and must be monotonic and
2-D plaid (as if produced by meshgrid).
div = divergence(U,V) assumes X and Y are determined by the expression:
[X Y] = meshgrid(1:n,1:m)
where [m,n] = size(U).
Examples
This example displays the divergence of vector volume data as slice planes
using color to indicate divergence.
load wind
div = divergence(x,y,z,u,v,w);
slice(x,y,z,div,[90 134],[59],[0]);
shading interp
daspect([1 1 1])
camlight
2-451
divergence
See Also
streamtube, curl, isosurface
2-452
dlmread
2dlmread
Purpose
Read an ASCII delimited file into a matrix
Graphical
As an alternative to dlmread, use the Import Wizard. To activate the Import
Interface
Wizard, select Import data from the File menu.
Syntax
M = dlmread(filename,delimiter)
M = dlmread(filename,delimiter,R,C)
M = dlmread(filename,delimiter,range)
Description
M = dlmread(filename,delimiter) reads numeric data from the ASCII
delimited file filename, using the specified delimiter. A comma (,) is the
default delimiter. Use '\t' to specify a tab delimiter.
M = dlmread(filename,delimiter,R,C) reads numeric data from the ASCII
delimited file filename, using the specified delimiter. The values R and C
specify the row and column where the upper-left corner of the data lies in the
file. R and C are zero based so that R=0, C=0 specifies the first value in the file, which is the upper left corner.
M = dlmread(filename,delimiter,range) reads the range specified by
range = [R1 C1 R2 C2] where (R1,C1) is the upper-left corner of the data to
be read and (R2,C2) is the lower-right corner. range can also be specified using
spreadsheet notation as in range = 'A1..B7'.
Remarks
dlmread fills empty delimited fields with zero. Data files having lines that end
with a non-space delimiter, such as a semi-colon, produce a result that has an
additional last column of zeros.
See Also
dlmwrite, textread, csvread, csvwrite, wk1read, wk1write
2-453
dlmwrite
2dlmwrite
Purpose
Write a matrix to an ASCII delimited file
Syntax
dlmwrite(filename,M,delimiter)
dlmwrite(filename,M,delimiter,R,C)
Description
dlmwrite(filename,M,delimiter) writes matrix M into an ASCII-format file,
using delimiter to separate matrix elements. The data is written to the upper
left-most cell of the spreadsheet filename. A comma (,) is the default delimiter.
Use '\t' to produce tab-delimited files.
dlmwrite(filename,M,delimiter,R,C) writes matrix A into an ASCII-format
file, using delimiter to separate matrix elements. The data is written to the
spreadsheet filename, starting at spreadsheet cell R and C, where R is the row
offset and C is the column offset. R and C are zero based so that R=0, C=0
specifies the first value in the file, which is the upper left corner.
Remarks
The resulting file is readable by spreadsheet programs.
See Also
dlmread, csvwrite, csvread, wk1write, wk1read
2-454
dmperm
2dmperm
Purpose
Dulmage-Mendelsohn decomposition
Syntax
p = dmperm(A)
[p,q,r] = dmperm(A)
[p,q,r,s] = dmperm(A)
Description
If A is a reducible matrix, the linear system Ax = b can be solved by permuting A to a block upper triangular form, with irreducible diagonal blocks, and then
performing block backsubstitution. Only the diagonal blocks of the permuted
matrix need to be factored, saving fill and arithmetic in the blocks above the
diagonal.
p = dmperm(A) returns a row permutation p so that if A has full column rank,
A(p,:) is square with nonzero diagonal. This is also called a maximum
matching.
[p,q,r] = dmperm(A) where A is a square matrix, finds a row permutation p
and a column permutation q so that A(p,q) is in block upper triangular form.
The third output argument r is an integer vector describing the boundaries of
the blocks: The kth block of A(p,q) has indices r(k):r(k+1)-1.
[p,q,r,s] = dmperm(A), where A is not square, finds permutations p and q
and index vectors r and s so that A(p,q) is block upper triangular. The blocks
have indices (r(i):r(i+1)-1, s(i):s(i+1)-1).