how to determine frequency of analog write ?

if I have the following code that is writing to the pin3 with some delay, what would be the frequency of this signal?
and how can we change this frequency ?
oops forgot to paste the code

void setup()
{
pinMode(3,OUTPUT);
}

void loop()
{
for(int i =0;i < 100;i++)
{
analogWrite(3,i);
delay(50);
}
for(int i = 100;i > 0;i–)
{
analogWrite(3,i);
delay(50);
}
}

Looks like you left out the code...

The frequency won't change. It is fixed to approximately 490Hz.

When you give analogWrite() a different value, the duty cycle of the waveform changes. So the amount of time the signal is ON versus OFF changes, but those two times combined stay the same.

As the default state pins 5 & 6 run at 976.5Hz, using fast-PWM mode (phase varies
with modulation) at 8 bits resolution pins 9,10,11, 3 use 490.1 Hz phase-correct
PWM mode with 8 bits resolution. (Assuming a 16MHz clocked Arduino Uno or similar)

This can be recofigured by directly updating the hardware timers, but note that pins
5 and 6 use timer0 which is also used to drive mills(), micros() and delay(), so changing
that timer will break those functions.

Why do you want to change the frequency, normally this is not an issue.