This page contains tips for using Lua 4.0 with FEMM 4.2. Some of these are documented in FEMM help file (User's manual) but some are not.

Full LUA 4.0 documentation: http://www.lua.org/manual/4.0/

To insert a comment use two hyphens, at the beginning of a line or at the end of command:

-- this is a comment
x = x + 1;   -- this is also a comment 

The relational operators in Lua are

equal, not equal, smaller than, greater than, equal or smaller, equal or greater
  ==      ~=           <             >           <=                >=

Example of a FOR loop and an IF statement

for n=1,20 do
    -- Comment within FOR loop
    hi_analyze();
    hi_loadsolution();
    ho_savebitmap("T"..n..".bmp");
    ho_close();
 
        if (n<15) then
            mi_selectgroup(1)
            mi_movetranslate(0,0.1)
        end -- end of IF
 
end  -- end of FOR loop

There is no need to pre-declare the “counting” variable (“n” in the example above). It gets declared at the point of use directly.

        if (n<15 and x>0) then
        end
        
        if (n<15 or x>0) then
        end

Some functions return multiple values.

Example: To catch all values at a point with coordinates (0.01,0) use:

A, B1, B2, Sig, E, H1, H2, Je, Js, Mu1, Mu2, Pe, Ph = mo_getpointvalues(0.01,0)

where the names before the = sign are all the variables to which the data will be transferred. If you are interested only in H1 and H2, use a dummy variables, which can be discarded, and leave others out, for example:

x1, x2, x3, x4, x5, H1, H2 = mo_getpointvalues(0.01,0)

To the exact format refer to the User's Manual in FEMM. The definitions of functions can change in newer updates.

• mo_getpointvalues(X,Y) Get the values associated with the point at x,y RETURN values in order

FEMM has certain constants defined, which can be used as inputs and will be evaluated correctly.

• PI = Pi = pi = 3.14159 - mathematical constant π
• uo = PI*4.e-7 - magnetic permeability of free space (lower case “u” and “o”, not zero)
• eo = 8.85418781762e-12 - electrical permittivity of free space (lower case “e” and “o”, not zero)

These are defined in the text file (use Notepad to open):

C:\femm42\bin\init.lua (or depending where FEMM was installed into).

Sometimes results need to be written into files whose numbers increase in a sequence. This can be achieved by using the structure as in the example below, where: “string”..n..“string” allows including the variable “n” in the name:

for n=1,10 do  -- FOR loop with "n" as the numerator
 
   -- write results to a sequentially numbered file
   handle1 = openfile("filename_"..n..".txt","w")   -- w = rewrite, a = append, r = read      
   write(handle1, variable_A, "\n")              -- write "variable_A" to the file   
   closefile(handle1)
 
  end
 
pause() -- this can be used for debugging

Lua in FEMM handles complex numbers automatically, for example:

a = 1 + I*2
b = 0.3 - I*0.4
a + b = 1.3 + I*1.6
a * b = 1.1 + I*0.2
a/b = -2 + I*4
re(b) = 0.3
im(b) = -0.4
abs(b) = 0.5