calculating forward kinematics using D-H matrix - robot

Question

I have a 6-DOF robot arm model:
robot arm structure
I want to calculate forward kinematics, so I uses the D-H matrix. the D-H parameters are:
static const std::vector<float> theta = {
0,0,90.0f,0,-90.0f,0};
// d
static const std::vector<float> d = {
380.948f,0,0,-560.18f,0,0};
// a
static const std::vector<float> a = {
-220.0f,522.331f,80.0f,0,0,94.77f};
// alpha
static const std::vector<float> alpha = {
90.0f,0,90.0f,-90.0f,-90.0f,0};
and the calculation :
glm::mat4 Robothand::armForKinematics() noexcept
{
glm::mat4 pose(1.0f);
float cos_theta, sin_theta, cos_alpha, sin_alpha;
for (auto i = 0; i < 6;i++)
{
cos_theta = cosf(glm::radians(theta[i]));
sin_theta = sinf(glm::radians(theta[i]));
cos_alpha = cosf(glm::radians(alpha[i]));
sin_alpha = sinf(glm::radians(alpha[i]));
glm::mat4 Ai = {
cos_theta, -sin_theta * cos_alpha,sin_theta * sin_alpha, a[i] * cos_theta,
sin_theta, cos_theta * cos_alpha, -cos_theta * sin_alpha,a[i] * sin_theta,
0, sin_alpha, cos_alpha, d[i],
0, 0, 0, 1 };
pose = pose * Ai;
}
return pose;
}
the problem I have is that, I can't get the correct result, for example, I want to calculate the transformation matrix from first joint to the 4th joint, I will change the for loop i < 3,then I can get the pose matrix, and I can the origin coordinate in 4th coordinate system by pose * (0,0,0,1).but the result (380.948,382.331,0) seems not correct because it should be move along x-axis not y-axis. I have read many books and materials about D-H matrix, but I can't figure out what's wrong with it.

Answer 1

I have figured it out by myself, the real problem behind is glm::mat, glm::mat is col-type which means columns will be initialized before rows,I changed the code and get the correct result:
for (int i = 0; i < joint_num; ++i)
{
pose = glm::rotate(pose, glm::radians(degrees[i]), glm::vec3(0, 0, 1));
pose = glm::translate(pose,glm::vec3(0,0,d[i]));
pose = glm::translate(pose, glm::vec3(a[i], 0, 0));
pose = glm::rotate(pose,glm::radians(alpha[i]),glm::vec3(1,0,0));
}
then I can get the position by:
auto pos = pose * glm::vec4(x,y,z,1);