I would like to evaluate a math string in my corona app. Right now I'm focusing on the trig functions, so let's let the example be the most difficult we're likely to face:
local expr = "2sin(4pi+2)+7"
My goal is for this to somehow be (either) evaluated as is with maybe a pi --> math.pi switch, or to even break it up. The breaking up would be much more difficult, however, since it COULD be as complicated a above, but could also just be sin(1).
So I would prefer to stay as close to the python eval(expr) function as possible, but if that can't happen, I am flexible.
The simplest way would be to replace sin with math.sin (pi with math.pi and so on), add missing multiplications signs, and run it through loadstring, but loadstring is not available in Corona environment.
This means you will need to write your own parser for these expressions. I found a discussion on Corona forums that may help you as a starting point: here, with some details and a demo here
This should do the trick, it is able to use the lua math functions without putting 'math.function' so just sqrt(100) works fine. I threw this together because I have seen this question asked way too many times. Hopes this helps :)
If you have any questions feel free to contact me at rayaman99#gmail.com
function evaluate(cmd,v) -- this uses recursion to solve math equations
--[[ We break it into pieces and solve tiny pieces at a time then put them back together
Example of whats going on
Lets say we have "5+5+5+5+5"
First we get this:
5+5+5+5 + 5
5+5+5 + 5
5+5 + 5
5 + 5
Take all the single 5's and do their opperation which is addition in this case and get 25 as our answer
if you want to visually see this with a custom expression, uncomment the code below that says '--print(l,o,r)'
]]
v=v or 0
local count=0
local function helper(o,v,r)-- a local helper function to speed things up and keep the code smaller
if type(v)=="string" then
if v:find("%D") then
v=tonumber(math[v]) or tonumber(_G[v]) -- This section allows global variables and variables from math to be used feel free to add your own enviroments
end
end
if type(r)=="string" then
if r:find("%D") then
r=tonumber(math[r]) or tonumber(_G[r]) -- A mirror from above but this affects the other side of the equation
-- Think about it as '5+a' and 'a+5' This mirror allows me to tackle both sides of the expression
end
end
local r=tonumber(r) or 0
if o=="+" then -- where we handle different math opperators
return r+v
elseif o=="-" then
return r-v
elseif o=="/" then
return r/v
elseif o=="*" then
return r*v
elseif o=="^" then
return r^v
end
end
for i,v in pairs(math) do
cmd=cmd:gsub(i.."(%b())",function(a)
a=a:sub(2,-2)
if a:sub(1,1)=="-" then
a="0"..a
end
return v(evaluate(a))
end)
end
cmd=cmd:gsub("%b()",function(a)
return evaluate(a:sub(2,-2))
end)
for l,o,r in cmd:gmatch("(.*)([%+%^%-%*/])(.*)") do -- iteration this breaks the expression into managable parts, when adding pieces into
--print(":",l,o,r) -- uncomment this to see how it does its thing
count=count+1 -- keep track for certain conditions
if l:find("[%+%^%-%*/]") then -- if I find that the lefthand side of the expression contains lets keep breaking it apart
v=helper(o,r,evaluate(l,v))-- evaluate again and do the helper function
else
if count==1 then
v=helper(o,r,l) -- Case where an expression contains one mathematical opperator
end
end
end
if count==0 then return (tonumber(cmd) or tonumber(math[cmd]) or tonumber(_G[cmd])) end
-- you can add your own enviroments as well... I use math and _G
return v
end
a=5
print(evaluate("2+2+2*2")) -- This still has work when it comes to pemdas; however, the use parentheses can order things!
print(evaluate("2+2+(2*2)"))-- <-- As seen here
print(evaluate("sqrt(100)"))
print(evaluate("sqrt(100)+abs(-100)"))
print(evaluate("sqrt(100+44)"))
print(evaluate("sqrt(100+44)/2"))
print(evaluate("5^2"))
print(evaluate("a")) -- that we stored above
print(evaluate("pi")) -- math.pi
print(evaluate("pi*2")) -- math.pi
Related
I'm building a moving and sensing bot in CoppelliaSim for school. CopelliaSim uses Lua for scripting. Basically every time the bot's forward sensors hit something, one of three if statements will run. I want it to count how many times any of these if statements runs, and once that count gets to a certain amount (like 20), I'll run something else, which will do the same thing (find collisions, add to the count, reach an amount, and switch back to the first).
i=0
result=sim.readProximitySensor(noseSensor) -- Read the proximity sensor
-- If we detected something, we set the backward mode:
if (result>0) then backUntilTime=sim.getSimulationTime()+3
print("Collision Detected")
i=i+1
print(i)
end
result=sim.readProximitySensor(noseSensor0) -- Read the proximity sensor
-- If we detected something, we set the backward mode:
if (result>0) then backUntilTime=sim.getSimulationTime()+3
print("Collision Detected")
i=i+1
print(i)
end
result=sim.readProximitySensor(noseSensor1) -- Read the proximity sensor
-- If we detected something, we set the backward mode:
if (result>0) then backUntilTime=sim.getSimulationTime()+3
print("Collision Detected")
i=i+1
print(i)
end
Above is the start of a function and one of the three If statements. I'm printing just to see if it actually increments. It is printing, but it is not incrementing (just 1 over and over). This bot has 3 sensors on it (an if statement for each sensor) and it adds 1 to i for the first collision and ignores the rest, even if it's from the same sensor. I feel like my problem is just some simple syntax issue with Lua that I don't know and can't find how to properly fix.
I'm happy to provide more code if this little snippet was not sufficient to answer this question.
Assuming that you have a looping function such as sysCall_actuation which is being executed per simulation step. As Joseph Sible-Reinstate Monica has already stated, you are setting your variable i back to zero every time a simulation step is executed. To achieve your goal, you would have to set your variable to 0 outside your function. There are two appropriate approaches to achieve that:
Define the variable outside any function, in the beginning of your file (or before you define any function that uses your variable e.g right before the definition of sysCall_actuation).
-- Beginning of the file.
local i = 0
..
function sysCall_actuation()
..
i = i + 1
..
end
Define your variable in sysCall_init function, which is the appropriate approach in CoppeliaSim.
function sysCall_init()
i = 0
..
end
Finally, you can use your variable in your sysCall_actuation function with basic comparison operations:
function sysCall_actuation()
..
if i > 20 then
i = 0 -- Reset 'i' so this function will not be running every step again and again.
-- Do something here.
..
end
As a side note, practice using local variables whenever you can, to keep the memory clean and avoid having ambiguous variables.
local times=0
function rTA(v)
times=times+1
if times % 3 <= 0 then
print(v)
end
end
or
local times=0
function rTA(v)
times=times+1
if times == 3 then
print(v)
times=0
end
end
rTA("N1")
rTA("N2")
rTA("N3")
rTA("N4")
rTA("N5")
rTA("N6")
rTA("N7")
rTA("N8")
rTA("N9")
They both return the same output (N3, N6, N9), but I can't seem to understand the difference in both of them..
As pointed out both are checking if "times" is multiple of 3, although the first version is a little more "elegant" it costs more in terms of processing. The second is a little less readable in terms of meaning (you can understand that it is trying to check for multiples of 3, but it is not a first sight thing, you have to think for a moment).
Cheers
I have a function in lua, which is given 2 vectors, return the lambda multiplier of first vector to second one, here is my code
function Math.vectorLambda( v1,v2 )
local v1Length,v2Length=math.sqrt(v1.x^2+v1.y^2),math.sqrt(v2.x^2+v2.y^2)
if v1Length==0 then
return nil
else
local dotProduct=v1.x*v2.x+v1.y*v2.y
print(dotProduct,v1Length,v2Length,math.abs(dotProduct)==(v1Length*v2Length))
if math.abs(dotProduct)==(v1Length*v2Length) then
if v1.x~=0 then
return v2.x/v1.x
else
return v2.y/v1.y
end
else
return nil
end
end
end
However, if
--this is what I get from terminal and I believe that it does not display the whole number--
v1={0.51449575542753,-0.85749292571254}
v2={-10,16.666666666667}
the output is
-19.436506316151 1 19.436506316151 false
which is saying the absolute value of dotProduct and v1Length*v2Length are not the same...
What is the reason for above, rather than I am blind? :(
BTW, the function is not stable..with exactly the same vectors, the function might has the same output except math.abs(dotProduct)==(v1Length*v2Length) gives true and hence return correct answer rather than nil, why?
Floats are tricky. You most likely have differences on the smaller decimal places (I don't know for sure, since I get true here). Try printing the numbers with a bigger precision, using a function like:
function prec_print(v, prec)
local format = '%.' .. prec .. 'f'
print(string.format(format, value))
end
In any case, you should almost never use == to compare floating point equality. For floats, it's quite easy to get false for simple things like a+b-b==a. What you should probably do is to check whether de difference of the two values is less than some threshold:
function almost_equal(float1, float2, threshold)
return math.abs(float1 - float2) <= threshold
end
But it's actually trickier than that (if, say, float1 and float2 are too far apart). Anyway, this read is mandatory for anyone working with floats: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
Cheers!
Im a amatuer at coding. So, mind me if i face palmed some things.
Anyways, im making a alpha phase for a OS im making right? I'm making my installer. Two questions. Can i get a code off of pastebin then have my lua script download it? Two. I put the "print" part of the code in cmd. I get "Illegal characters". I dont know what went wrong. Here's my code.
--Variables
Yes = True
No = False
--Loading Screen
print ("1")
sleep(0.5)
print("2")
sleep(0.5)
print("Dowloading OS")
sleep(2)
print("Done!")
sleep(0.2)
print("Would you like to open the OS?")
end
I see a few issues with your code.
First of all, True and False are both meaningless names - which, unless you have assigned something to them earlier, are both equal to nil. Therefore, your Yes and No variables are both set to nil as well. This isn't because true and false don't exist in lua - they're just in lowercase: true and false. Creating Yes and No variables is redundant and hard to read - just use true and false directly.
Second of all, if you're using standard lua downloaded from their website, sleep is not a valid function (although it is in the Roblox version of Lua, or so I've heard). Like uppercase True and False, sleep is nil by default, so calling it won't work. Depending on what you're running this on, you'll want to use either os.execute("sleep " .. number_of_seconds) if you're on a mac, or os.execute("timeout /t " .. number_of_seconds) if you're on a PC. You might want to wrap these up into a function
function my_sleep_mac(number_of_seconds)
os.execute("sleep " .. number_of_seconds)
end
function my_sleep_PC(number_of_seconds)
os.execute("timeout /t " .. number_of_seconds)
end
As for the specific error you're experiencing, I think it's due to your end statement as the end of your program. end in lua doesn't do exactly what you think it does - it doesn't specify the end of the program. Lua can figure out where the program ends just by looking to see if there's any text left in the file. What it can't figure out without you saying it is where various sub-blocks of code end, IE the branches of if statements, functions, etc. For example, suppose you write the code
print("checking x...")
if x == 2 then
print("x is 2")
print("Isn't it awesome that x is 2?")
print("x was checked")
lua has no way of knowing whether or not that last statement, printing the x was checked, is supposed to only happen if x is 2 or always. Consequently, you need to explicitly say when various sections of code end, for which you use end. For a file, though, it's unnecessary and actually causes an error. Here's the if statement with an end introduced
print("checking x...")
if x == 2 then
print("x is 2")
print("isn't it awesome that x is 2?")
end
print("x was checked")
although lua doesn't care, it's a very good idea to indent these sections of code so that you can tell at a glance where it starts and ends:
print("checking x...")
if x == 2 then
print("x is 2")
print("isn't it awesome that x is 2?")
end
print("x was checked")
with regards to your "pastebin" problem, you're going to have to be more specific.
You can implement sleep in OS-independent (but CPU-intensive) way:
local function sleep(seconds)
local t0 = os.clock()
repeat
until os.clock() - t0 >= seconds
end
I just started with Lua as part of a school assignment. I'd like to know if there's an easy way to implement profiling for Lua? I need something that displays allocated memory, variables in use regardless of their type, etc.
I've been finding C++ solutions which I have been able to compile successfully but I don't know how to import them to the Lua environment.
I also found Shinny but I couldn't find any documentation about how to make it work.
There are several profilers available that you can check, but most of them target execution time (and are based on debug hook).
To track variables, you will need to use debug.getlocal and debug.getupvalue (from your code or from debug hook).
To track memory usage you can use collectgarbage(count) (probably after collectgarbage(collect)), but this only tells you total memory in use. To track individual data structures, you may need traverse global and local variables and calculate the amount of space they take. You can check this discussion for some pointers and implementation details.
Something like this would be the simplest profiler that tracks function calls/returns (note that you should not trust absolute numbers it generates, only relative ones):
local calls, total, this = {}, {}, {}
debug.sethook(function(event)
local i = debug.getinfo(2, "Sln")
if i.what ~= 'Lua' then return end
local func = i.name or (i.source..':'..i.linedefined)
if event == 'call' then
this[func] = os.clock()
else
local time = os.clock() - this[func]
total[func] = (total[func] or 0) + time
calls[func] = (calls[func] or 0) + 1
end
end, "cr")
-- the code to debug starts here
local function DoSomethingMore(x)
x = x / 2
end
local function DoSomething(x)
x = x + 1
if x % 2 then DoSomethingMore(x) end
end
for outer=1,100 do
for inner=1,1000 do
DoSomething(inner)
end
end
-- the code to debug ends here; reset the hook
debug.sethook()
-- print the results
for f,time in pairs(total) do
print(("Function %s took %.3f seconds after %d calls"):format(f, time, calls[f]))
end