Monte Carlo map's given?

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Hi to all,

I'm trying to program a Monte Carlo Localization. I know the algorithm steps. 1-Initizalization (particles and pose robot) 2-Sensor update (get lidar data, matching with the map and give weights to each particle) 3-Resampling related to weight. 3-Motion update (move particles related to odometry sensor) 4-Sensor update and so on.

My problem is in step 2. I don't know how to do the matching with the map with sensor data... I don't know the equation or how to do it. So my question is how to give weight to particles with a map given.

Any help?

Thanks a lot.