可以发现最终结果只和 $a[1][1], a[1][2], a[2][1]$ 有关，因为所有的以 $(1, 1)$ 为左上角的矩形都至少经过 $a[1][2]$ 或者 $a[2][1]$ ，所以把 $a[1][1]$ 作为最大值，其它两个点作为最小的两个值；或者把 $a[1][1]$ 作为最小值，其它两个点作为最大的两个值。这两种情况分别计算，并不是等价的。设 $n > m$，那么最大差的个数是 $n(m - 1)$ 或者 $m(n - 1)$，因为 $n > m$，所以 $m(n - 1) > n(m - 1)$。

// Date: Wed Dec 20 21:02:01 2023

#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <algorithm>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

const int INF = 0x3f3f3f3f, MOD = 1e9 + 7;
const double eps = 1e-8;
const int dir[8][2] = {
    {0, 1}, {0, -1}, {1, 0}, {-1, 0}, {1, 1}, {1, -1}, {-1, 1}, {-1, -1},
};

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> VI;
typedef pair<int, int> PII;

const ull Pr = 131;

#define For(i, a, b) for (int i = int(a); i < int(b); ++i)
#define Rof(i, a, b) for (int i = int(b) - 1; i >= int(a); --i)
#define For1(i, a, b) for (int i = int(a); i <= int(b); ++i)
#define Rof1(i, a, b) for (int i = int(b); i >= int(a); --i)
#define ForE(i, j) for (int i = h[j]; i != -1; i = ne[i])

#define f1 first
#define f2 second
#define pb push_back
#define has(a, x) (a.find(x) != a.end())
#define nonempty(a) (!a.empty())
#define all(a) (a).begin(), (a).end()
#define SZ(a) int((a).size())

template <typename t> istream &operator>>(istream &in, vector<t> &vec) {
  for (t &x : vec)
    in >> x;
  return in;
}

template <typename t> ostream &operator<<(ostream &out, vector<t> &vec) {
  int n = SZ(vec);
  For(i, 0, n) {
    out << vec[i];
    if (i < n - 1)
      out << ' ';
  }
  return out;
}

#ifdef _DEBUG
#define debug1(x) cout << #x " = " << x << endl;
#define debug2(x, y) cout << #x " = " << x << " " #y " = " << y << endl;
#define debug3(x, y, z)                                                        \
  cout << #x " = " << x << " " #y " = " << y << " " #z " = " << z << endl;
#else
#define debug1
#define debug2
#define debug3
#endif

const int N = 10010;
int t, a[N], n, m;

int main(void) {
#ifdef _DEBUG
  freopen("1825b.in", "r", stdin);
#endif
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);

  cin >> t;

  while (t--) {
    cin >> n >> m;

    int m1 = n * m;
    For(i, 0, m1) { cin >> a[i]; }

    sort(a, a + m1);

    int x = a[m1 - 1], y = a[0], y1 = a[1], d1 = x - y, d2 = x - y1;

    if (n < m)
      swap(n, m);

    ll res = d1 * (n - 1) * m + d2 * (m - 1);

    x = a[0], y = a[m1 - 1], y1 = a[m1 - 2], d1 = y - x, d2 = y1 - x;
    ll res1 = d1 * (n - 1) * m + d2 * (m - 1);

    res = max(res, res1);

    cout << res << '\n';
  }

  return 0;
}