Help with if condition

Solar2D Lua Language
#1

Hi all,

I am very new with lua and my question could be stupid, but I don’t know how to solve my problem.

Basically I use lua language to givo special commands to another code for ion beam transport.

I have created a code to produce particles with an exponential energy distribution and it works fine.

What I want to do now is to add a cut-off to avoid that particle with energy aboove a certain value will be produced but I am not able to do that.

The code I use is:

&nbsp; -- Generate Exponential distributed random variable with parameter lambda. local rand = simion.rand local ln = math.log function exponential\_rand() &nbsp; return -ln(rand())/0.44 end ------------------------ &nbsp; -- if&nbsp; exponential\_rand()\*1e6 \< 8.9\*1e6 then &nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; function my\_dist() &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return exponential\_rand()\*1e6&nbsp; --\< 8.9\*1e6 -- end &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; end ----------------------- local t = {coordinates=0} for i=1,2000 do &nbsp; local ke = my\_dist() &nbsp; t[#t+1] = standard\_beam { &nbsp;&nbsp;&nbsp; n = 10, &nbsp;&nbsp;&nbsp; tob = 0, &nbsp;&nbsp;&nbsp; mass = 1.00727647, &nbsp;&nbsp;&nbsp; charge = 1, &nbsp;&nbsp;&nbsp; ke = ke, &nbsp;&nbsp;&nbsp; cwf = 1, &nbsp;&nbsp;&nbsp; color = 0, &nbsp;&nbsp;&nbsp; direction = &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cone\_direction\_distribution { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; axis = vector(0, 0, 1), &nbsp; &nbsp;&nbsp; half\_angle = - 6.188e-9\*(ke\*1e-6)^6 +2.155e-6\*(ke\*1e-6)^5 -0.0002876\*(ke\*1e-6)^4 + 0.01799\*(ke\*1e-6)^3 -0.497\*(ke\*1e-6)^2 + 3.215\*(ke\*1e-6)+ 69.44, &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; fill = true &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }, &nbsp;&nbsp;&nbsp; position = gaussian3d\_distribution { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; mean = vector(0, 0, 0), &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; stdev = vector(0.06, 0.06, 0) &nbsp;&nbsp;&nbsp; } &nbsp; } end particles(t) &nbsp;

I try to add the if condition in the second block of the code, but it has no effect, can you help me with that?

Thak you in advance

#2

Hey schillacif,

don’t know if you solved the problem already, but I think the solution is rather trivial.

I assume the function simion.rand returns a random number?

If yes, the problem is, that you are not returning the random number that you are checking for.

Additionally the function “my_dist” is set globally, which isn’t great idea in most cases.

Might try something like this:

local rand = simion.rand local ln = math.log local multiplicator = 1e6 local cutOff = 8.9 local function exponential\_rand() return -ln(rand())/0.44 end local function my\_dist() local randomNumber = exponential\_rand() if randomNumber \<= cutOff then return randomNumber\*multiplicator else return cutOff\*multiplicator end end local t = {coordinates=0} for i=1,2000 do local ke = my\_dist() t[#t+1] = standard\_beam { n = 10, tob = 0, mass = 1.00727647, charge = 1, ke = ke, cwf = 1, color = 0, direction = cone\_direction\_distribution { axis = vector(0, 0, 1), half\_angle = - 6.188e-9\*(ke\*1e-6)^6 +2.155e-6\*(ke\*1e-6)^5 -0.0002876\*(ke\*1e-6)^4 + 0.01799\*(ke\*1e-6)^3 -0.497\*(ke\*1e-6)^2 + 3.215\*(ke\*1e-6)+ 69.44, fill = true }, position = gaussian3d\_distribution { mean = vector(0, 0, 0), stdev = vector(0.06, 0.06, 0) } } end particles(t)
#3

Hey schillacif,

don’t know if you solved the problem already, but I think the solution is rather trivial.

I assume the function simion.rand returns a random number?

If yes, the problem is, that you are not returning the random number that you are checking for.

Additionally the function “my_dist” is set globally, which isn’t great idea in most cases.

Might try something like this:

local rand = simion.rand local ln = math.log local multiplicator = 1e6 local cutOff = 8.9 local function exponential\_rand() return -ln(rand())/0.44 end local function my\_dist() local randomNumber = exponential\_rand() if randomNumber \<= cutOff then return randomNumber\*multiplicator else return cutOff\*multiplicator end end local t = {coordinates=0} for i=1,2000 do local ke = my\_dist() t[#t+1] = standard\_beam { n = 10, tob = 0, mass = 1.00727647, charge = 1, ke = ke, cwf = 1, color = 0, direction = cone\_direction\_distribution { axis = vector(0, 0, 1), half\_angle = - 6.188e-9\*(ke\*1e-6)^6 +2.155e-6\*(ke\*1e-6)^5 -0.0002876\*(ke\*1e-6)^4 + 0.01799\*(ke\*1e-6)^3 -0.497\*(ke\*1e-6)^2 + 3.215\*(ke\*1e-6)+ 69.44, fill = true }, position = gaussian3d\_distribution { mean = vector(0, 0, 0), stdev = vector(0.06, 0.06, 0) } } end particles(t)