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/**
 * Computes the Parabolic SAR, as originally developed by Welles Wilder.
 *
 * @param array $his Extreme Points: The highest high
 * @param array $los Extreme Points: The lowest low
 * @param float $afInc Acceleration Factor Increment, for each time point
 *   Lower increment = less sensitive (indicitive)
 * @param float $afMax Acceleration Factor Max, rno matter how long the trend
 *   Lower max step = less sensitive (reactive)
 * @param bool $withDir Indicates if trend direction should be returned.
 * @return array 
 *  If $withDir is true, result is tuple of length 2.
 *    Tuple contains ( array of SAR values, array of trend direction )
 *  Else if $withDir is false, result is simply an array of SAR values.
 */
function parabolicSAR($his,$los,$afInc=0.02,$afMax=0.20,$withDir=false) {
 if( !is_array($his) || !is_array($los) ) {
   trigger_error("First 2 parameters must be arrays: his, los",E_USER_WARNING);
   return ($withDir) ? array(false,false) : false;
 }
 if( count($his) != count($los) ) { 
   trigger_error("Arrays must be equal length.", E_USER_ERROR);
   return ($withDir) ? array(false,false) : false;
 }
 if( count($his) < 2 ) { 
   return ($withDir) ? array(array(),array()) : array();
 }
 
 $keys = array_keys($his);
 $his = array_values($his);
 $los = array_values($los);
 
 // Initialize trend to whatever
 $trend = ($his[1]>=$his[0] || $los[0]<=$los[1]) ? +1 : -1;
 
 // Previous SAR: Use first data point&#039;s extreme value, depending on trend
 $pSAR = ($trend>0) ? $los[0] : $his[0];
 
 // Extreme point: Highest during uptrend || lowest during downtrend
 $EP = ($trend>0) ? $his[0] : $los[0];
 
 // Acceleration factor
 $AF = $afInc;
 
 // Initialize results based on trend guess
 $r = array($keys[0] => $pSAR);   // SAR Results
 $d = array($keys[0] => $trend);  // Trend Directions
 
 // Compute "tomorrow" SAR
 for($i=1,$n=count($keys)-1; $i<$n; $i++) {
   // Do for uptrend
   if( $trend > 0 ) { 
 
     // Making higher highs: accelerate
     if( $his[$i] > $EP ) {
       $EP = $his[$i];
       $AF = min($afMax,$AF+$afInc);
     }
 
     // Tomorrow&#039;s SAR based on today&#039;s price action.
     $nSAR = $pSAR + $AF * ($EP - $pSAR);
 
     // Rule: SAR can never be above prior period&#039;s low or the current low.
     $nSAR = ($i>0) ? min($los[$i],$los[$i-1],$nSAR) : min($los[$i],$nSAR);
 
     // Rule: If SAR crosses tomorrow&#039;s price range, the trend switches.
     if( $nSAR > $los[$i+1] ) { 
       $trend = -1;
       $nSAR = $EP;      // set to the last EP recorded on the previous trend
       $EP = $los[$i+1]; // reset accordingly to this period&#039;s maximum
       $AF = $afInc;     // reset to its initial value of 0.02.
     }
 
   } else {
   // Do for downtrend
 
     // Making lower lows: accelerate
     if( $los[$i] < $EP ) { 
       $EP = $los[$i];
       $AF = min($afMax,$AF+$afInc);
     }
 
     // Tomorrow&#039;s SAR based on today&#039;s price action.
     $nSAR = $pSAR + $AF * ($EP - $pSAR);
 
     // Rule: SAR can never be below prior period&#039;s highs or the current high.
     $nSAR = ($i>0) ? max($his[$i],$his[$i-1],$nSAR) : max($his[$i],$nSAR);
 
     // Rule: If SAR crosses tomorrow&#039;s price range, the trend switches.
     if( $nSAR < $his[$i+1] ) {
       $trend = +1;
       $nSAR = $EP;      // set to the last EP recorded on the previous trend
       $EP = $his[$i+1]; // reset accordingly to this period&#039;s maximum
       $AF = $afInc;     // reset to its initial value of 0.02.
     }
 
   } // end: if uptrend else downtrend
 
   $r[$keys[$i+1]] = $nSAR;
   $d[$keys[$i+1]] = $trend;
   $pSAR = $nSAR;
 } // END: for(i..n)
 
 return ($withDir) ? array($r,$d) : $r;
} // END: function parabolicSAR($his,$los,$afInc=0.02,$afMax=0.20)

Sources:

• StockCharts.com: Chart School
• Wikipedia: Parabolic SAR

PHP Parse error: syntax error, unexpected T_STRING in /var/www/default/docs/out/lib/lib/_php---obj---FFT.php.html on line 1, referer:...

I wanted script.php.html to be treated as an HTML file and not be processed by the php engine.  This double-extension was causing me grief.  The docs claimed that only files ending in the extension will be handled by the AddHandler command.  I was incredulous of this claim, especially in light of Apache’s ability to do content negotiation with those .var language files.

Q: Why was this happening? I first guessed it may have been due to mod_mime, but quickly ruled that out.  I then guessed it was the MultiView option… Maybe, this is one mechanism that governs content negotiation… The documentation claims:

# The index.html.var file (a type-map) is used to deliver content-
# negotiated documents.  The MultiViews Option can be used for the
# same purpose, but it is much slower.

This statement lead me to suspect that my problem may actually be caused by an issue with the AddHandler option, since an AddHandler command must be executed to associate type-map with that .var extension.

Ah me, time is money, and in the end, I actually didn’t diagnose the problem, but I did discover (by trial and error) a workaround.

In file /etc/httpd/conf.d/php.conf, I surrounded

AddHandler php5-script .php
AddType text/html .php

with

<Files ~ "\.php$">
  AddHandler php5-script .php
  AddType text/html .php
</Files>

Now, only files explicitly ending in “.php” will be treated as a php5-script.  Take that!

Together, to be cross-version compliant:

putenv("TZ=America/Los_Angeles");
if( function_exists("date_default_timezone_set") ) { 
 date_default_timezone_set("America/Los_Angeles");
}

We need both to be reverse-compatible with PHP4.

The only named entities for XML are &, > and <. For all others you need to use the Unicode character code (eg.  ). Webkit: Entity ‘nbsp’ not defined – Convert HTML entities to XML

These worked for me:

error_reporting = E_ALL
display_errors = stderr
display_startup_errors = On
log_errors = Off
html_errors = Off
;error_log = php-errors.log

Ensure that error_log is not set, otherwise error will not be displayed. This problem may be related, but is obviously not, the date bug mentioned in the PHP bug reports. It may be fixed in the latest snapshot. As a note, the php.ini date.timezone setting is date.timezone = "Pacific/Honolulu", and I still had this problem.

Other things I noticed:
When error_log = syslog, you can find the PHP events in the windows Event Viewer -> Windows Logs -> Application. I mention it in case you want that type of thing… or think error that logging may not be working.

Here’s the work-around:

if( -1 <= $py && $py <= 1 ) {
  // Undocumented PHP bug when Y coordinate is zero.
  imageFilledEllipse($img,$px,$py,$X,$X,$color);
  imageFilledRectangle($img,$px-$halfX,$py-1,$px+$halfX,$py+1,$color);
} else {
  imageFilledEllipse($img,$px,$py,$X,$X,$color);
}

PHP Version:

PHP 4.3.9 (cgi) (built: Apr  1 2009 10:41:42)
Copyright (c) 1997-2004 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies

$ yum search php-gd

php-gd.i386                              4.3.9-3.26             installed
Matched from:
php-gd
The php-gd package contains a dynamic shared object that will add
support for using the gd graphics library to PHP.

Question: How much do you need to zoom before the points are clearly distinguishable?

Let us arbitrarily define the criteria for distinguishability as an icon of 25 pixels in size. This icon, it can be said, has a radius of 13 pixels. In reality, icon size is a function of your viewport’s size. I leave that up to you to calculate.

Let us define the scale of the map as the absolute width of the map (in map units) divided by the width of the view port. As an example, let’s use the Earth’s longitude range: -180 to +180 degrees, but in a global Mercator projection. The coordinate range of longitude for this map is [-20037508,+20037508) meters. Our viewport has a range of [0,255] pixels (viewport units). The scale of this map in this viewport is (2*20037508)/256. Be careful not to double-count +20037508, as -20037508 = +20037508 and would yield an improper scale. The viewport size is an integer and does not wrap; there are no fractions of a pixel in a viewport.

We shall now define a target scale. The target scale is the desired scale of the map that allows our icons to become viewable. Our example will use buildings having a foot print of 300 meters (map units) in width and depth. Our target scale, therefore, is 300/25 = 12 meters per pixel.

Question: How much do we need to zoom in before our buildings are distinguishable?

Implementation 1 (naive, iterative):

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function zoomLevel( $maprange, $viewport, $distFactor=0.10, $zoomFactor=2 ) {
  // $viewport = 256;
  // $maprange = 2*M_PI*6378137;
  $scale = $maprange / $viewport;
 
  // 10% of viewport required to distinguish an icon.
  $target = $distFactor * $viewport;
 
  $zoom = 0;
  while ( $scale > $target ) {
    $zoom += 1;
    $scale /= $zoomFactor;
  }
  return $zoom;
}

Implementations 2, 3 and 4:

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function zoomLevel( $maprange, $viewport, $distFactor=0.10, $zoomFactor=2 ) {
  $scale = $maprange / $viewport;
  $target = $distFactor * $viewport;
 
  // naive log
  return ceil( (log($scale)/log($zoomFactor) - log($target)/log($zoomFactor)) );
 
  // commutative log
  return ceil( (log($scale) - log($target)) / log($zoomFactor) );
 
  // subtraction property of logs (best implementation)
  return ceil( log($scale/$target)/log($zoomFactor) );
}

In order to be able to simply dl(“Datascope.so”) in your PHP code, you first need to make sure Datascope.so is compiled and copied to the extension_dir, as specified in php.ini (ex: /usr/lib/php4).

Answer:
No: Stop right now. You’re not qualified to read this article.
Yes: Keep reading.

Notes

You’re not compiling the PHP source code for actual use, so please don’t install it. If you do, you run the risk of clobbering any pre-existing php installations, and overwriting previously compiled-in modules. The only reason why you ”make” PHP is so that the Zend libraries are properly initialized.

The PHP ”make” step may be avoidable, but given that the compile doesn’t affect system performance, I didn’t bother.

Paths should be changed to reflect your setup. If you don’t have the src/contrib/data/php/datascope code, you can get it from the contrib source at BRTT‘s web site.

Contrib appears to be maintained by Indiana University.

Paths

• Antelope Bash Script ”/opt/antelope/4.9/setup.sh”
• Datascope Source ”/opt/antelope/4.9/src/contrib/data/php/datascope”
• PHP Source Code URL ”http://downloads.php.net/ilia/php-5.1.4.tar.bz2”
• PHP Modules Directory ”/usr/lib/php/modules/”

Compile and Install Steps

1. wget <PHP Source Code>
2. bunzip2 php-5.1.4.tar.bz2
3. tar xf php-5.1.4.tar
4. cd php-5.1.4
5. PHP_INC=`pwd`
6. export PHP_INC
7. ./configure
8. make
9. cd <Datascope Source>
10. source <Antelope Bash Script>
11. sudo make install
12. sudo cp Datascope.so <PHP Modules Directory>

PHP Script Example

Proper usage of the ”Datascope.so” module follows:

putenv( "PFPATH=/opt/antelope/4.9/data/pf" );
putenv( "ANTELOPE=/opt/antelope/4.9" );
 
set_include_path(
  get_include_path().PATH_SEPARATOR.getenv('ANTELOPE')."/data/php"
);
 
 
if( !extension_loaded( "Datascope.so" ) ) {
  dl( "Datascope.so") || exit( "Failed to load datascope.so" ) ;
}