From a560d4c0097d66bed34e832dc70fa0ef4be86006 Mon Sep 17 00:00:00 2001
From: Brandon Rodriguez <brodriguez8774@gmail.com>
Date: Sat, 30 Nov 2019 01:37:18 -0500
Subject: [PATCH] Add various small bugfixes for "pivot" function
It now properly handles more cases.
---
resources/simplex/pivot.py | 135 +++++++++++++++++++++++++++++--------
1 file changed, 108 insertions(+), 27 deletions(-)
diff --git a/resources/simplex/pivot.py b/resources/simplex/pivot.py
index 875cf7e..3a25f2b 100644
--- a/resources/simplex/pivot.py
+++ b/resources/simplex/pivot.py
@@ -34,7 +34,12 @@ class Pivot():
self._basic_var_indexes = None
self._nonbasic_var_indexes = None
- def __call__(self, old_basic_col, new_basic_col, *args, **kwargs):
+ def __call__(self, old_basic_col, new_basic_col, *args, debug=False, **kwargs):
+ # Optionally override parent debug setting on call.
+ orig_debug = self._debug
+ if debug is True:
+ self._debug = debug
+
# Get parent data at the point of call.
self._matrix_a = self._parent._matrix_a
self._vector_b = self._parent._vector_b
@@ -44,7 +49,12 @@ class Pivot():
self._nonbasic_var_indexes = self._parent._n_array
# Run pivot function.
- return self.pivot(old_basic_col, new_basic_col)
+ results = self.pivot(old_basic_col, new_basic_col)
+
+ # Reset original debug settings.
+ self._debug = orig_debug
+
+ return results
def pivot(self, old_basic_col, new_basic_col):
"""
@@ -92,6 +102,8 @@ class Pivot():
# Compute updated objective function.
vector_c, obj_const_index = self._update_objective(
n_array,
+ matrix_a,
+ vector_b,
vector_c,
obj_const_index,
old_basic,
@@ -126,32 +138,38 @@ class Pivot():
logger.info(' vector_b: {0}'.format(vector_b))
logger.info(' old_basic: {0}'.format(old_basic))
logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
# Calculate our new constraint constant.
- vector_b[new_basic[0]] = self._vector_b[new_basic[0]] / self._matrix_a[old_basic[0]][new_basic[1]]
-
- # Truncate if can be represented as int.
- if vector_b[new_basic[0]] % 1 == 0:
- vector_b[new_basic[0]] = int(vector_b[new_basic[0]])
+ vector_b[new_basic[0]] = self._truncate_if_int(
+ self._vector_b[new_basic[0]] / self._matrix_a[old_basic[0]][new_basic[1]]
+ )
# Loop through all nonbasic indexes (minus the one we're adding). Adjust coefficients in matrix.
for col_index in n_array:
-
- # Make sure to skip the one we're adding.
- if col_index != new_basic[1]:
+ # Make sure to skip the one we're removing.
+ if col_index != old_basic[1]:
# Adjust given coefficient.
- matrix_a[new_basic[0]][col_index] = self._matrix_a[old_basic[0]][col_index] / self._matrix_a[old_basic[0]][new_basic[1]]
-
- # Truncate if can be represented as int.
- if matrix_a[new_basic[0]][col_index] % 1 == 0:
- matrix_a[new_basic[0]][col_index] = int(matrix_a[new_basic[0]][col_index])
+ matrix_a[new_basic[0]][col_index] = self._truncate_if_int(
+ self._matrix_a[old_basic[0]][col_index] / self._matrix_a[old_basic[0]][new_basic[1]]
+ )
# Separately adjust the index of the newly nonbasic variable.
- matrix_a[new_basic[0]][old_basic[1]] = self._matrix_a[old_basic[0]][old_basic[1]] / self._matrix_a[old_basic[0]][new_basic[1]]
+ matrix_a[new_basic[0]][old_basic[1]] = self._truncate_if_int(1 / self._matrix_a[old_basic[0]][new_basic[1]])
+
+ # Check if new basic is negative. If so, flip.
+ if matrix_a[new_basic[0]][new_basic[1]] == -1:
+ matrix_a[new_basic[0]][new_basic[1]] = 1
- # Truncate if can be represented as int.
- if matrix_a[new_basic[0]][old_basic[1]] % 1 == 0:
- matrix_a[new_basic[0]][old_basic[1]] = int(matrix_a[new_basic[0]][old_basic[1]])
+ # Optional debugging printout.
+ if self._debug:
+ logger.info('Updated Pivot._calculate_new_basic()')
+ logger.info(' n_array: {0}'.format(n_array))
+ logger.info(' matrix_a: {0}'.format(matrix_a))
+ logger.info(' vector_b: {0}'.format(vector_b))
+ logger.info(' old_basic: {0}'.format(old_basic))
+ logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
return (matrix_a, vector_b)
@@ -173,6 +191,7 @@ class Pivot():
logger.info(' vector_b: {0}'.format(vector_b))
logger.info(' old_basic: {0}'.format(old_basic))
logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
# Loop through all basic indexes (minus the one we're removing). Adjust coefficients in matrix.
for row_index in range(len(vector_b)):
@@ -180,23 +199,41 @@ class Pivot():
# Make sure to skip the one we're removing.
if row_index != old_basic[0]:
# Adjust constraint constants.
- vector_b[row_index] = self._vector_b[row_index] - (self._matrix_a[row_index][new_basic[1]] * self._vector_b[old_basic[0]])
+ vector_b[row_index] = self._truncate_if_int(
+ self._vector_b[row_index] - (self._matrix_a[row_index][new_basic[1]] * vector_b[old_basic[0]])
+ )
# Loop through all nonbasic indexes.
for col_index in n_array:
# Adjust coefficient.
- matrix_a[row_index][col_index] = self._matrix_a[row_index][col_index] - (self._matrix_a[new_basic[0]][col_index] * self._matrix_a[row_index][new_basic[1]])
+ matrix_a[row_index][col_index] = self._truncate_if_int(
+ self._matrix_a[row_index][col_index] - (matrix_a[new_basic[0]][col_index] * self._matrix_a[row_index][new_basic[1]])
+ )
# Separately adjust the index of the newly nonbasic variable. Make sure to skip the new basic variable.
if row_index != new_basic[0]:
- matrix_a[row_index][old_basic[1]] = self._matrix_a[row_index][old_basic[1]] - (self._matrix_a[new_basic[0]][old_basic[1]] * self._matrix_a[row_index][new_basic[1]])
+ matrix_a[row_index][old_basic[1]] = self._truncate_if_int(
+ self._matrix_a[row_index][old_basic[1]] - (matrix_a[new_basic[0]][old_basic[1]] * self._matrix_a[row_index][new_basic[1]])
+ )
+
+ # Optional debugging printout.
+ if self._debug:
+ logger.info('Updated Pivot._compute_coefficients()')
+ logger.info(' n_array: {0}'.format(n_array))
+ logger.info(' matrix_a: {0}'.format(matrix_a))
+ logger.info(' vector_b: {0}'.format(vector_b))
+ logger.info(' old_basic: {0}'.format(old_basic))
+ logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
return (matrix_a, vector_b)
- def _update_objective(self, n_array, vector_c, obj_const_index, old_basic, new_basic):
+ def _update_objective(self, n_array, matrix_a, vector_b, vector_c, obj_const_index, old_basic, new_basic):
"""
Computes updated objective function.
:param n_array: Array of all non-basic variable col indexes.
+ :param matrix_a: Matrix of variable coefficients for constraint equations.
+ :param vector_b: Vector of constants for constraint equations.
:param vector_c: Vector of objective function coefficients and constant.
:param obj_const_index: Index of constant in vector_c.
:param old_basic: Tuple of (row, col) index values for old basic variable.
@@ -207,21 +244,40 @@ class Pivot():
logger.info('')
logger.info('Starting Pivot._update_objective()')
logger.info(' n_array: {0}'.format(n_array))
+ logger.info(' matrix_a: {0}'.format(matrix_a))
+ logger.info(' vector_b: {0}'.format(vector_b))
logger.info(' vector_c: {0}'.format(vector_c))
logger.info(' obj_const_index: {0}'.format(obj_const_index))
logger.info(' old_basic: {0}'.format(old_basic))
logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
# Update objective constant.
- vector_c[self._obj_constant_index] = self._vector_c[self._obj_constant_index] - (self._vector_b[new_basic[0]] * self._vector_c[new_basic[1]])
+ vector_c[self._obj_constant_index] = self._truncate_if_int(
+ self._vector_c[self._obj_constant_index] - (vector_b[new_basic[0]] * self._vector_c[new_basic[1]])
+ )
# Loop through all nonbasic indexes.
for col_index in n_array:
# Adjust objective function value.
- vector_c[col_index] = self._vector_c[col_index] - (self._matrix_a[new_basic[0]][col_index] * self._vector_c[new_basic[1]])
+ vector_c[col_index] = self._truncate_if_int(
+ self._vector_c[col_index] - (matrix_a[new_basic[0]][col_index] * self._vector_c[new_basic[1]])
+ )
# Separately adjust the index of the newly nonbasic variable.
- vector_c[old_basic[1]] = self._vector_c[old_basic[1]] - (self._matrix_a[new_basic[0]][old_basic[1]] * self._vector_c[new_basic[1]])
+ vector_c[old_basic[1]] = self._truncate_if_int(
+ self._vector_c[old_basic[1]] - (matrix_a[new_basic[0]][old_basic[1]] * self._vector_c[new_basic[1]])
+ )
+
+ # Optional debugging printout.
+ if self._debug:
+ logger.info('Updated Pivot._update_objective()')
+ logger.info(' n_array: {0}'.format(n_array))
+ logger.info(' vector_c: {0}'.format(vector_c))
+ logger.info(' obj_const_index: {0}'.format(obj_const_index))
+ logger.info(' old_basic: {0}'.format(old_basic))
+ logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
return (vector_c, obj_const_index)
@@ -236,11 +292,12 @@ class Pivot():
# Optional debugging printout.
if self._debug:
logger.info('')
- logger.info('Starting Pivot._update_objective()')
+ logger.info('Starting Pivot._compute_basic_sets()')
logger.info(' n_array: {0}'.format(n_array))
logger.info(' b_array: {0}'.format(b_array))
logger.info(' old_basic: {0}'.format(old_basic))
logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
# Remove new basic variable from set of nonbasics.
n_array.remove(new_basic[1])
@@ -255,4 +312,28 @@ class Pivot():
# Add new basic variable to set of basics, making sure we put it in the proper equation index.
b_array.insert(new_basic[0], new_basic[1])
+ # Optional debugging printout.
+ if self._debug:
+ logger.info('Updated Pivot._compute_basic_sets()')
+ logger.info(' n_array: {0}'.format(n_array))
+ logger.info(' b_array: {0}'.format(b_array))
+ logger.info(' old_basic: {0}'.format(old_basic))
+ logger.info(' new_basic: {0}'.format(new_basic))
+ logger.info('')
+
return (n_array, b_array)
+
+ def _truncate_if_int(self, value):
+ """
+ Truncates value if it can be properly represented as an int.
+
+ Necessary since we're dealing with multiplication and division, which will return floats by default.
+ :param value: Possible float value to truncate to an int.
+ :return: Proper representation of value.
+ """
+ if value == 0.0 or value % 1 == 0:
+ # Can be represented as an int. Return that.
+ return int(value)
+ else:
+ # Return original representation.
+ return value
--
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