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SparseArray

SparseArray
yields a sparse array in which values appear at positions .
SparseArray
yields the same sparse array.
SparseArray[list]
yields a sparse array version of list.
SparseArray
yields a sparse array representing a array.
SparseArray
yields a sparse array in which unspecified elements are taken to have value val.
  • By default, SparseArray takes unspecified elements to be .
  • Normal gives the ordinary array corresponding to a sparse array object.
  • The position specifications can contain patterns.
  • Rules of the form Band[...]->vals specify values on bands in the sparse array.
  • With rules the are evaluated separately for each set of indices that match .
  • SparseArray[list] requires that list be a full array, with all parts at a particular level being lists of the same length.
  • The individual elements of a sparse array cannot themselves be lists.
  • SparseArray[rules] yields a sparse array with dimensions exactly large enough to include elements whose positions have been explicitly specified.
  • List and matrix operations are typically set up to work as they do on Normal.
  • Functions with attribute Listable are automatically threaded over the individual elements of the ordinary arrays represented by SparseArray objects.
  • Part extracts specified parts of the array represented by a SparseArray object, rather than parts of the SparseArray expression itself.
  • Functions like Map are automatically applied to components in a SparseArray object.
  • SparseArray is treated as a raw object by functions like AtomQ and for purposes of pattern matching.
  • Dimensions gives the dimensions of a sparse array.
  • The standard output format for a sparse array indicates the number of nondefault elements and the total dimensions.
Construct a sparse matrix with values at only a few specified positions:
View it as a matrix:
Convert it to an ordinary dense matrix:
Construct a sparse matrix with values at only a few specified positions:
In[1]:=
Click for copyable input
Out[1]=
View it as a matrix:
In[2]:=
Click for copyable input
Out[2]//MatrixForm=
Convert it to an ordinary dense matrix:
In[3]:=
Click for copyable input
Out[3]=
Make a large sparse vector matrix and depth-3 array:
Construct a tridiagonal matrix using patterns for indices:
Construct a 10,000 by 10,000 version:
Make a sparse diagonal matrix:
This is equivalent to DiagonalMatrix:
Except that as a sparse matrix, it uses much less memory:
Construct a block diagonal matrix using rules with Band:
Convert an ordinary matrix into a sparse matrix:
Make a rank-4 sparse tensor with values at random positions:
ArrayRules produces the minimal list of rules needed to specify the SparseArray:
Many typical operations work with SparseArray objects as they would for equivalent lists:
Arithmetic works element-wise just as it does for lists:
Matrix products are done with Dot:
Many linear algebra functions are done efficiently with the sparse form:
Many other list commands work automatically:
The unspecified elements can have any value:
Symbolic values can be replaced with local definitions:
Construct a sparse matrix with all machine-number values:
Construct a sparse matrix with exact integer values:
N[s] is the same as :
Create a list with a single nonzero element:
Plot a list of rules:
Represent a network with an adjacency matrix:
Solve a boundary-value problem using finite differences:
A SparseArray object is Equal to the corresponding ordinary list:
They are not SameQ because the expression structure is different:
For functions f that work with SparseArray objects, typically f[s]==f[Normal[s]]:
This includes all functions with the attribute Listable:
Convert linear expressions to SparseArray objects using CoefficientArrays:
Convert from SparseArray to expressions using Dot:
If a position is repeated in the rule list for SparseArray, the first instance is used:
SparseArray objects can represent data too large to represent in normal form:
Using Normal will give a :
Sparse operations do not by default check for cancellation:
Use SparseArray to recompute the sparse structure:
Operations with side effects may give different values when iterating over SparseArray:
With Reap and Sow you can see what elements are accessed:
For a SparseArray object, Part gives parts of the represented list:
The FullForm is a way of reconstructing the object from basic storage information:
It should not be necessary, but if you want, you can get pieces of the full form with patterns:
A SparseArray object is treated as atomic for functions that do not work on the representation:
Cases does not work on the represented matrix:
You can often use the result of ArrayRules to get the information without expanding:
The game of life:
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