Q:

Calculating a mass resistance to acceleration

Im not sure if this is the right place for this question, but I need to calculate the velocity of a large amplitude pendulum, with my current code it results in a sinusoidal graph.
The problem is that the period of the pendulum becomes smaller if I increase the mass, which shouldn't happen in a real pendulum because the period is independent of mass; The acceleration increases with mass but resistance to acceleration does too, and I don't know how to code this.
I have tried looking into angular momentum but my knowledge of physics is very limited. I have this:
long double timeFrame = 0.01;
    if(getNewAngle==true)
{
    //Convert to radians.
    myAngle = Angle*M_PI/180;
    getNewAngle = false;
    //Velocity starts at 0.
    myVelocity = 0;
}
//Setup starting variables.
long double dLength = std::stod(Length,0);
long double dGravity = std::stod(Gravity,0);
long double dMass = std::stod(Mass,0);
long double dPeriod = std::stod(Period,0);

//Large amplitude pendulum acceleration formula
long double dAcceleration = -dMass*dGravity/dLength*sin(myAngle);
//Angular displacement formula;
long double dDisplacement = myVelocity*timeFrame+0.5*dAcceleration*pow(timeFrame,2);
myVelocity = dDisplacement/timeFrame;
myAngle = myAngle + dDisplacement;

A:

This:
//Large amplitude pendulum acceleration formula
long double dAcceleration = -dMass*dGravity/dLength*sin(myAngle);

is incorrect. It should be this:
//Large amplitude pendulum acceleration formula
long double dAcceleration = -dGravity/dLength*sin(myAngle);

That's right, mass doesn't enter into it (unless you start to consider air resistance).

