Mandelbrot sample code (if statement issue)

[Csaba]

Hi,

I have an issue with the line

if .calc(x/40, y/40)  # error: here

in the code below. The error message is:

error: COBRA INTERNAL ERROR / FallThroughException / info=TruthExpr-sh(12369, didBindInh=false, didBindInt=false, didStartBindImp=true, didBindImp=false, token=Token(DOT, '.', '.', ln 18, col 9, Mandelbrot.cobra), Treatment=AsIs, type=nil, 12369)

If I replace the if .calc…. with if .doIt (a dummy Boolean function), I get the same compiler error. So what is the correct Cobra syntax here?

Regards
Csaba

# See <!-- m --><a class="postlink" href="http://www.timestretch.com/FractalBenchmark.html">http://www.timestretch.com/FractalBenchmark.html</a><!-- m -->
# 2009-01-13 Csaba Urbaniczky
# if .calc( x/40 , y/40) does not compile
class Program 
    const bailOut as int = 16  
    const maxIterations as int = 1000  
    
    def doIt as Boolean is shared
        return true
        
    def mandelbrot is shared
        try
            print 'Rendering'
            for y as int in -39 :39 : 1 
                print 
                for x as int in -39 :39 : 1
                    # if .doIt , print '*', stop  # give same kind of  error
                    if .calc(x/40, y/40)  # error: here
                        print '*', stop 
                    else 
                        print ' ' , stop
        catch ex as Exception
            print 'mandelbrot EXCEPTION: [ex]'

    def calc(ci as number,   y as number) as Boolean is shared
        try
            cr as decimal = y-0.5
            zr as decimal = 0.0
            zi as decimal = 0.0
            for i as int in  0 : .maxIterations :1
                zr2  = zr * zr
                zi2 = zi * zi
                if zi2 + zr2 > .bailOut, return false 
                temp = zr * zi 
                zr = zr2 - zi2 + cr 
                zi = temp + temp + ci
            return true
        catch ex as Exception
            print 'calc EXCEPTION: [ex]'
            return true

    def main is shared
        try
            print 'Cobra Mandelbrot Start [ DateTime.now]'
            startTime= DateTime.now
            .mandelbrot
            print
            print 'Cobra elepsed [DateTime.now.subtract(startTime)] seconds'
        catch ex as Exception
            print 'main EXCEPTION: [ex]'

[Charles]

I don't see anything wrong with your syntax and even if there was, Cobra should always give an error instead of an exception.

I'll take a look.

In the mean time, try changing Boolean to bool and see if that helps.

[Charles]

Yeah, that's it. Change to "bool" and the problem will go away.

I'll fix up the compiler. Btw, if you're doing timings, a couple considerations:

-- Setting up exception handlers may slow down code. At least when your program stabilizes, you may wish to remove your exception handlers. You can also leave them out anyway as they will print if you experience an uncaught exception at run-time.

-- On .NET, the most accurate way to measure time is using a Stopwatch which has a finer granularity than DateTime. In Cobra that would be:

use System.Diagnostics

...
        sw = Stopwatch()
        sw.start
...
        sw.stop
        print sw.elapsedMilliseconds

You can look up the docs on it for more details.

I'll be interested to see your final version if you'd like to post it. Maybe we can include it as a sample. I'm also curious to run it on Mono vs. .NET on the same hardware.

[Charles]

Oh and your final timing should be done with "cobra -turbo ...". See "cobra -h" for info.

[Csaba]

Hi,

Here is the working Mandelbrot sample with some of my timing. Feel free to use it as a sample.

I did not care about the -turbo optimization, since the Cobra version with float is surprisingly faster than same example in the VB.net code. The try-catch did not impose any measurable penaltie in this example so I kept it. Note the speed difference between using float and decimal. The Ruby (v1.8.6) version requires 22 s (but I think Ruby is using decimal). I havn't tried Python.

Regards
Csaba

# See <!-- m --><a class="postlink" href="http://www.timestretch.com/FractalBenchmark.html">http://www.timestretch.com/FractalBenchmark.html</a><!-- m -->
# 2009-03-09 Csaba Urbaniczky
# 2009-03-09  Test in SciTE 
#       With  float:: 48-128 ms (in SciTE)
#       With  float & Try Catch  &:48-128 ms  = same!
#       With decimal & Try Catch  6.05 - 6.06 s = very much slower!
#      VB.NET 2005 version on the same computer: 175-180 ms
class Program 
    const bailOut as int = 16  
    const maxIterations as int = 1000  
            
    def mandelbrot is shared
        try
            print 'Rendering'
            for y as int in -39 :39 : 1 
                print 
                for x as int in -39 :39 : 1
                    if .calc(x/40f, y/40f)  # error: here
                        print '*', stop 
                    else 
                        print ' ' , stop
        catch ex as Exception
            print 'mandelbrot EXCEPTION: [ex]'

    def calc(ci as float,  y as float) as bool is shared
        try
            cr as float = y-0.5f
            zr as float = 0.0f
            zi as float= 0.0f
            for i as int in  0 : .maxIterations :1
                zr2  = zr * zr
                zi2 = zi * zi
                if zi2 + zr2 > .bailOut, return false 
                temp as float = zr * zi 
                zr = zr2 - zi2 + cr 
                zi = temp + temp + ci
            return true
        catch ex as Exception
            print 'calc EXCEPTION: [ex]'
            return true

    def main is shared
        try
            print 'Cobra Mandelbrot Start [DateTime.now]'
            sw = System.Diagnostics.Stopwatch() 
            sw.start        
            .mandelbrot
            sw.stop 
            print
            print 'Cobra elapsed: [sw.elapsedMilliseconds] ms'
        catch ex as Exception
            print 'main EXCEPTION: [ex]'

[Charles]

Thanks for posting this. I'll definitely incorporate it.

[Charles]

I've added this in Cobra under Samples/. Thanks.

I trimmed out some of the explicit types and use "number" type instead of "float" or "decimal" with the "number" set in a directive above. I feel this represents the canonical Cobra style. The timing wasn't changed.

[Charles]

Oh and I added some more warnings and error checking to Cobra to avoid the problems that you originally ran into.

[Csaba]

Hi,
EDIT: Nice! I’m looking forward to Cobra 1.0 and when Cobra has support in SharpDevelop.

I have now tested this Mandelbrot sample code also with Ruby 1.9.1 and Pyton 3.0.1. The summary so far on my computer is:

Cobra 0.8 float Time / s: 0.09 Rel time: 1
Cobra 0.8 float and Try Catch Time / s: 0.09 Rel time: 1
VB 2005 Time / s: 0.18 Rel time: 2
Python 3.01 Time / s: 3.3 Rel time: 37
Cobra 0.8 decimal Time / s: 6.1 Rel time: 68
Ruby 1.9.1 Time / s: 11.5 Rel time: 128
Ruby 1.8.6 Time / s: 22.0 Rel time: 244

(Impossible to align – spaces disappears)
For other examples, see http://www.timestretch.com/FractalBenchmark.html

Regards
Csaba

[jonathandavid]

Hi,
EDIT: Nice! I’m looking forward to Cobra 1.0 and when Cobra has support in SharpDevelop.

I have now tested this Mandelbrot sample code also with Ruby 1.9.1 and Pyton 3.0.1. The summary so far on my computer is:

Cobra 0.8 float Time / s: 0.09 Rel time: 1
Cobra 0.8 float and Try Catch Time / s: 0.09 Rel time: 1
VB 2005 Time / s: 0.18 Rel time: 2
Python 3.01 Time / s: 3.3 Rel time: 37
Cobra 0.8 decimal Time / s: 6.1 Rel time: 68
Ruby 1.9.1 Time / s: 11.5 Rel time: 128
Ruby 1.8.6 Time / s: 22.0 Rel time: 244

(Impossible to align – spaces disappears)
For other examples, see http://www.timestretch.com/FractalBenchmark.html

Regards
Csaba

That's funny, I wouldn't have expected the decimal version to be so far behind. Chuck, are decimal operations really >50 times slower that their float counterparts?