Find a specific pair in Matrix maximum value of mat(c, d) – mat(a, b) over all choices of indexes s

'''
Given an n x n matrix mat[n][n] of integers, find the maximum value of mat(c, d) – mat(a, b) over all choices of indexes such that both c > a and d > b
'''

def findMaxValue(mat, n):
    dp=[[float('inf')]*n for i in range(n)]
    dp[0][0]=mat[0][0]#This is min for matrix 0,0 to (1,1)
    ans=float('-inf')
    #dp[i][j] stores minimum from 0,0 to i-1,j-1 rectangle

    for i in range(n):
        for j in range(n):
            if i>=1:
                dp[i][j]=min(dp[i][j],dp[i-1][j],mat[i][j])
            if j>=1:
                dp[i][j]=min(dp[i][j],dp[i][j-1],mat[i][j])
            if i>=1 and j>=1:
                ans=max(ans,mat[i][j]-dp[i-1][j-1])#minimum of (i-1,j-1)'s rectangle at dp[i][j] i.e. 0,0 to (i-1,j-1) is stored at dp[i][j]
    return ans