edu.stanford.math.plex4.homology.utility

Class HomologyUtility

java.lang.Object

edu.stanford.math.plex4.homology.utility.HomologyUtility

public class HomologyUtility
extends java.lang.Object

This class contains static utility functions to aid the homology computations.

Author:

Andrew Tausz

Constructor Summary

Constructors

Constructor and Description
HomologyUtility()

Method Summary

Methods

Modifier and Type	Method and Description
static int[]	appendToArray(int[] array, int newValue) This function appends the argument newValue to the end of the supplied array.
static int	compareIntArrays(int[] array1, int[] array2) This function performs a comparison of two arrays of ints.
static gnu.trove.TIntHashSet	computeIntersection(gnu.trove.TIntHashSet set1, gnu.trove.TIntHashSet set2) This function computes the intersection between two sets of integers.
static int[]	convertIndices(int[] vertices, int[] conversionArray)
static Simplex	convertIndices(Simplex simplex, int[] conversionArray)
static int[]	deconvertIndices(int[] vertices, int[] conversionArray)
static int[]	getDefaultBoundaryCoefficients(int length) This function returns the standard sequence of boundary coefficients used in simplicial homology, defined by c_i = (-1)^i.
static int[]	lowerEntries(int[] array, int k) This function returns the first k entries of the supplied array.
static int[]	removeIndex(int[] array, int index) This function returns a new array which contains the same entries as the supplied array except that the element at the specified index has been removed and the proceeding elements have been shifted down by one.
static int[]	upperEntries(int[] array, int k) This function returns the last entries of the supplied array starting from the index k.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HomologyUtility

public HomologyUtility()

Method Detail

getDefaultBoundaryCoefficients

public static int[] getDefaultBoundaryCoefficients(int length)

This function returns the standard sequence of boundary coefficients used in simplicial homology, defined by c_i = (-1)^i. For small values of the desired length, it returns a precomputed array. This optimization is performed because this operation is done very often during homology and cohomology calculations. Also, almost all calls to this function will involve small values of the argument length, since most of the homological features of interest are in low dimensions. Nevertheless, this function will return the desired sequence even if the cache is not populated with the desired array.

Parameters:

length - the length of the array to get

Returns:

an array of with specified length containing the numbers (-1)^i

compareIntArrays

public static int compareIntArrays(int[] array1,
                   int[] array2)

This function performs a comparison of two arrays of ints. It returns a positive value if the first array is greater than the second, a negative value if the first array is less than the second, and zero if they are equal. The comparison is done as follows. First the lengths are compared. If they are unequal, then it returns the comparison of the lengths. If the array lengths are equal, it performs a dictionary comparison starting from the 0-th entry in the arrays.

Parameters:

array1 - the first array parameter

array2 - the second array parameter

Returns:

1 if array1 > array2, 0 if array1 == array2, -1 if array1 < array2

removeIndex

public static int[] removeIndex(int[] array,
                int index)

This function returns a new array which contains the same entries as the supplied array except that the element at the specified index has been removed and the proceeding elements have been shifted down by one.

Parameters:

array -

index -

Returns:

the array with the element at the specified index removed

appendToArray

public static int[] appendToArray(int[] array,
                  int newValue)

This function appends the argument newValue to the end of the supplied array. It does not modify the passed in array.

Parameters:

array - the array to append to

newValue - the value to append

Returns:

the supplied array with newValue appended

lowerEntries

public static int[] lowerEntries(int[] array,
                 int k)

This function returns the first k entries of the supplied array.

Parameters:

array -

k -

Returns:

the subarray array[0, ..., k]

upperEntries

public static int[] upperEntries(int[] array,
                 int k)

This function returns the last entries of the supplied array starting from the index k.

Parameters:

array -

k -

Returns:

the subarray array[k, ..., array.length - 1]

computeIntersection

public static gnu.trove.TIntHashSet computeIntersection(gnu.trove.TIntHashSet set1,
                                        gnu.trove.TIntHashSet set2)

This function computes the intersection between two sets of integers.

Parameters:

set1 - the first set

set2 - the second set

Returns:

a TIntSet containing elements common to both input sets

convertIndices

public static Simplex convertIndices(Simplex simplex,
                     int[] conversionArray)

convertIndices

public static int[] convertIndices(int[] vertices,
                   int[] conversionArray)

deconvertIndices

public static int[] deconvertIndices(int[] vertices,
                     int[] conversionArray)