if statement runtime error C++

running my C++ code, I originally had 3 equations. Pu, Pm & Pd. It ran fine. Once I introduced the If statement, with variations on the 3 equations, depending on the loop iteration, I receive a runtime error. Any help would be appreciated.

Cheers in advance.

#include <cmath>
#include <iostream>
#include <vector>
#include <iomanip>


int Rounding(double x)
{
    int Integer = (int)x;
    double Decimal = x - Integer;

    if (Decimal > 0.49)
    {
        return (Integer + 1);
    }
    else
    {
        return Integer;
    }
}

int main()
{
double a = 0.1;
double sigma = 0.01;
int delta_t = 1;
double M = -a * delta_t;
double V = sigma * sigma * delta_t;
double delta_r = sqrt(3 * V);
int count;

double PuValue;
double PmValue;
double PdValue;

int j_max;
int j_min;

j_max = Rounding(-0.184 / M);
j_min = -j_max;

std::vector<std::vector<double>> Pu((20), std::vector<double>(20)); 
std::vector<std::vector<double>> Pm((20), std::vector<double>(20)); 
std::vector<std::vector<double>> Pd((20), std::vector<double>(20)); 

std::cout << std::setprecision(10); 
for (int i = 0; i <= 2; i++)
    {
        count = 0;
        for (int j = i; j >= -i; j--)   
            {
                count = count + 1;
                if (j = 2) // Exhibit 1C
                {   
                    PuValue = 7.0/6.0 + (j * j * M * M + 3 * j * M)/2.0;
                    PmValue = -1.0/3.0 - j * j * M * M - 2 * j * M;
                    PdValue = 1.0/6.0 + (j * j * M * M + j * M)/2.0;
                }   
                else if (j = j_min) // Exhibit 1B
                {   
                    PuValue = 1.0/6.0 + (j * j * M * M - j * M)/2.0;
                    PmValue = -1.0/3.0 - j * j * M * M + 2 * j * M;
                    PdValue = 7.0/6.0 + (j * j * M * M - 3 *  j * M)/2.0;
                }   
                else
                {
                    PuValue = 1.0/6.0 + (j * j * M * M + j * M)/2.0;
                    PmValue = 2.0/3.0 - j * j * M * M;
                    PdValue = 1.0/6.0 + (j * j * M * M - j * M)/2.0;
                }
                Pu[count][i] = PuValue;
                Pm[count][i] = PmValue;
                Pd[count][i] = PdValue;

                std::cout << Pu[count][i] << ", ";
            }
        std::cout << std::endl;
    }
return 0;
}