我有一个函数可以在方格上生成（伪）随机游走，其中游走不应超出该正方形的边界，完整功能如下：
/**
* @brief Performs a single random walk returning the final distance from the origin
*
* Completes a random walk on a square lattice using the mersenne twister engine based pseudo-random
* number-generator (PRNG). The walk will not breach the boundaries of the square size provided to
* the function. The random walk starts at the origin and ends after some parameterised number of steps.
* Position co-ordinates of the walk for each iteration are sent to an output file.
*
* @param squareSideLength Length of square lattice side
* @param steps Number of steps to compute random walk up to
* @param engine Mersenne Twister engine typedef (used for generating random numbers locally)
* @param distribution Default distribution of random walk
* @param outputFile [Default nullptr] Pointer to file to write co-ordinate data of random walk to
* @return final distance of the particle from the origin
*/
double randomWalkSquareLattice(int squareSideLength, int steps, std::mt19937& engine, std::uniform_real_distribution<double>& distribution, std::ofstream* outputFile = nullptr) {
// store the half-length of the square lattice
const int halfSquareLength = squareSideLength / 2;
// initialise co-ordinates to the origin
double positionX = 0.0;
double positionY = 0.0;
// assign the default distribution to distDefault
std::uniform_real_distribution<double> distDefault = distribution;
// loop over a number of iterations given by the steps parameter
for (int i = 0; i < steps; i++) {
std::cout << positionX << "\t" << positionY << std::endl;
// if the x-position of the particle is >= to positive
// half square lattice length then generate decremental
// random number (avoiding breaching the boundary)
if (positionX >= halfSquareLength) {
double offset = positionX - halfSquareLength;
std::cout << std::endl << offset << std::endl;
std::uniform_real_distribution<double> distOffset(-offset, -1.0);
positionX += distOffset(engine);
}
// else if the x-position of the particle is <= to negative
// half square lattice length then generate incremental random
// number (avoiding breaching the boundary)
else if (positionX <= -halfSquareLength) {
double offset = std::abs(positionX + halfSquareLength);
std::cout << std::endl << offset << std::endl;
std::uniform_real_distribution<double> distOffset(offset, 1.0);
positionX += distOffset(engine);
}
// else (in case where x-position of particle is not touching
// the lattice boundary) generate default random number
else {
positionX += distDefault(engine);
}
// if the y-position of the particle is >= to positive
// half square lattice length then generate decremental
// random number (avoiding breaching the boundary)
if (positionY >= halfSquareLength) {
double offset = positionY - halfSquareLength;
std::cout << std::endl << offset << std::endl;
std::uniform_real_distribution<double> distOffset(-offset, -1.0);
positionY += distOffset(engine);
}
// else if the y-position of the particle is <= to negative
// half square lattice length then generate incremental
// random number (avoiding breaching the boundary)
else if (positionY <= -halfSquareLength) {
double offset = std::abs(positionY + halfSquareLength);
std::cout << std::endl << offset << std::endl;
std::uniform_real_distribution<double> distOffset(offset, 1.0);
positionY += distOffset(engine);
}
// else (in case where y-position of particle is not touching
// the lattice boundary) generate default random number
else {
positionY += distDefault(engine);
}
// if an outputFile is supplied to the function, then write data to it
if (outputFile != nullptr) {
*outputFile << positionX << "\t" << positionY << std::endl;
}
}
// compute final distance of particle from origin
double endDistance = std::sqrt(positionX*positionX + positionY*positionY);
return endDistance;
}
在方法中看到的条件阻止步行离开边界。但是，当使用足够数量的步骤调用它时（以便执行这些条件中的任何一个），我收到一条错误消息：
invalid min and max arguments for uniform_real
请注意，我发送给这个函数的 dist 是：
std::uniform_real_distribution<double> dist(-1.0,1.0);
因此（从打印到终端的值可以看出）问题不在于偏移量将永远大于在任何条件情况下给予 distOffset 的最大值。
问题是我不能给 u_r_d 一个任意精度的双精度值吗？还是我缺少其他东西？
编辑：我应该补充一点，这些是 main() 中使用的值：
int main(void) {
std::uniform_real_distribution<double> dist(-1.0, 1.0);
std::random_device randDevice;
std::mt19937 engine(randDevice());
//std::cout << dist(engine) << std::endl;
// Dimensions of Square Lattice
const int squareLength = 100;
// Number of Steps in Random Walk
const int nSteps = 10000;
randomWalkSquareLattice(squareLength, nSteps, engine, dist);
}