python - Creating a 2 x 2 matrix and finding its inverse -

class multidimensionalarray:  def __init__(self, numrows, numcolumns):     self.r = numrows     self.c = numcolumns      self.array = [[(x+3*y) x in range(self.r)] y in range(self.c)]              self.inverse = [[]]  def modifyitem(self, row, column, item):     self.array[row][column] = item  def getitem(self, row, column):     print self.array[row][column]     return self.array[row][column]  def showarray(self):     print self.array  def changesize(self, rows, columns):     self.r = rows     self.c = columns     self.array = [[(x+3*y) x in range(self.r)] y in range(self.c)]  def getsize(self):     print [self.r, self.c]     return [self.r, self.c]  def getinverse(self):      if ((self.r == 2) , (self.c == 2)):         = self.array[0][0]         b = self.array[0][1]         c = self.array[1][0]         d = self.array[1][1]          l in self.array:             item in l:                 item = int(item)          self.inverse[0][0] = d         self.inverse[0][1] = b * (-1)         self.inverse[1][0] = c * (-1)         self.inverse[1][1] =          self.inverse = self.inverse * (1 / (a*d - b*c))         print self.inverse         return self.inverse   mat = multidimensionalarray(2,2) mat.showarray() mat.getinverse() 

this code gets stuck on following lines of code. error says "list assignment index out of range". goal make mathematical inverse of given 2x2 matrix. can me working? thanks

self.inverse[0][0] = d self.inverse[0][1] = b * (-1) self.inverse[1][0] = c * (-1) self.inverse[1][1] = 

there 2 bugs.

first, define inverse self.inverse = [[]]. has no element [0][0], hence exception. may write instead self.inverse = [[0] * numcolumns in range(numrows)] initialize inverse 0 matrix.

the program fail on line self.inverse = self.inverse * (1 / (a*d - b*c)): python not know how multiply list number. 1 way be

k = 1 / (a*d - b*c) self.inverse = [[x * k x in u] u in self.inverse] 

notice b * (-1) can written -b.

apart that, class bit ugly, answer computed inverse correct. ugly, because matrix class not initialize predefined constant matrix, , inverse matrix, not member. guess there tests prepare better , more complete class.

---

to multiply elements of self.inverse "in place" (that is, without building new matrix):

for in range(numrows):     j in range(numcolumns):         self.inverse[i][j] *= k 

you may this:

for row in self.inverse:     j in range(numcolumns):         row[j] *= k