====== LUA scripting tips ======
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/

===== Comments =====
To insert a comment use two hyphens, at the beginning of a line or at the end of command: 
<code lua>
-- this is a comment
x = x + 1;   -- this is also a comment 
</code>

===== FOR loop and IF statement =====

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
<code lua>
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
</code>

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

===== The functions of AND and OR =====
<code>
        if (n<15 and x>0) then
        end
        
        if (n<15 or x>0) then
        end
</code>
===== Multiple output values of function =====
Some functions return multiple values. 

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

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

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:

<code>x1, x2, x3, x4, x5, H1, H2 = mo_getpointvalues(0.01,0)</code>

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

^ Symbol ^ Definition ^
| A | vector potential A or flux φ | 
| B1 | flux density Bx if planar, Br if axisymmetric |
| B2 | flux density By if planar, Bz if axisymmetric |
| Sig | electrical conductivity σ |
| E | stored energy density |
| H1 | field intensity Hx if planar, Hr if axisymmetric |
| H2 | field intensity Hy if planar, Hz if axisymmetric |
| Je | eddy current density | 
| Js | source current density |
| Mu1 | relative permeability μx if planar, μr if axisymmetric |
| Mu2 | relative permeability μy if planar, μz if axisymmetric |
| Pe | Power density dissipated through ohmic losses |
| Ph | Power density dissipated by hysteresis |

===== Constants in FEMM =====
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).

===== Sequential file names =====
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:

<code lua>
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
</code>

{{page>insert/paypal}}

===== Complex numbers =====
Lua in FEMM handles complex numbers automatically, for example:
<code lua>
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
</code>

===== Automatic limits in colour maps =====
Full command executed with just the legend parameter set to -1 shows default limits for the legend. This seems to work in pure LUA, and mo_showdensityplot(-1) does not work even in pure LUA:

<code lua>
mo_showdensityplot(legend,gscale,upper_B,lower_B,type)
mo_showdensityplot(-1,0,0,1,"bmag") 
</code>

legend: Set to 0 to hide the plot legend or 1 to show the plot legend.

(note that: ''mo_showdensityplot(-1)'' will not work).
  

===== Rounding in LUA =====
Rounding does not appear to be immediately available in LUA 4.0. Teh

<code lua>
function round_LUA(var_input, round_precision)

var_floor = floor(var_input/round_precision)*round_precision
var_ceil = ceil(var_input/round_precision)*round_precision
var_rounded = var_floor
 
if (var_input > (var_floor + 5*round_precision/10) ) then
var_rounded = var_ceil
end

return(var_rounded)

end -- end function

var_input = 123.44900000003   -- input variable to be rounded
round_precision = 10     -- rounding precision, use: 100, 10, 1, 0.1, 0.01 etc.

var_output = round_LUA(var_input, round_precision)

print(var_input)
print(var_output)

</code>