LTspice Monte Carlo Analysis Clarifications required

Question

I am learning about LTspice MC analysis from this site. I understood almost all the things except the below one.

"Then make another spice directive to execute a Monte Carlo run as below .step param run 1 100 1 The above syntax means that we are going to run the simulation for 100 times with starting point at 1 and the increment is 1. " My question here is,

What we are incrementing with a value of one. Here all the tolerances are fixed. (Please correct me if I am wrong).

Is this something like in the 1st iteration we take resistor value as R = R+Tolerance and in 2nd it is like R-Tolerance, something like that.

Are they running 100 permutation and combination like this:

Answer 1

What we are incrementing with a value of one.

You are incrementing the parameter run which is a public/global and special variable for LTspice's internal use.

Is this something like in the 1st iteration we take resistor value as R = R+Tolerance and in 2nd it is like R-Tolerance, something like that?

No. mc() function is something like a random generator between the given boundaries with a uniform distribution. In your circuit, at each iteration, each resistor will have a random value within the range set by their minimum possible and maximum possible values (i.e. in \$[R(1-tolb), R(1+tolb)]\$ range).

The simulation requires a dummy iterator, hence the parameter run driven by .step param function.

And this function takes the parameter run (as stated before, a special variable for LTspice, just like time) as input, so you need to manually increment it at reach iteration so that the random generator doesn't generate the same value. That is what .step param function does.

^{CORRECTION: run is not a global variable. In one of my earlier simulations in the past I used run as a parameter for my random generator. That's probably where my confusion comes from. Sorry for the wrong information.}