<?php
$PI = +3.1415;
$DT = 0.02;
$accgraphname = "kobens.txt";
$C = 10; $K=1000; $M = 4;

$i=0;
$Ag = array();
if (file_exists($accgraphname)){
    $lines = file($accgraphname);
    foreach($lines as $line){
        $line = trim($line);
        if (!empty($line)){
            list($dt, $ac) = explode(",", $line);
            $Ag[$i] = $ac;
            $i++;
        }
    }
}

$wd = sqrt(4*$K*$M-$C*$C)/(2*$M);
$Cc = 2*sqrt($K*$M);
$zi = $C/$Cc;
$Td = 2*$PI/$wd;
//$wd = sqrt(4*$K*$M-($zi*$zi*4*$K*$M))/(2*$M);
//$wd = sqrt($K/$M*(1-$zi*$zi));
//$wd*$wd/(1-$zi*$zi) = $K/$M;

$k = $M/($DT*$DT)+$C/(2*$DT);
$a = $M/($DT*$DT)-$C/(2*$DT);
$b = $K-2*$M/($DT*$DT);
$p = array();
while($val = each($Ag)){
    $p[] = $val[1]*$M;
}
$u[0] = 0; $u[1] = $p[0]-$b*$u[0];
$n = count($Ag);
$umin=$umax=0;
for ($i=1; $i<$n; $i++) {
    $u[$i+1] = ($p[$i]-$a*$u[$i-1]-$b*$u[$i])/$k;
    if ($umin > $u[$i+1])
        $umin = $u[$i+1];
    if ($umax < $u[$i+1])
        $umax = $u[$i+1];
};

$imgfile = "xydata.txt";
$imgw = 680;
$imgh = 200;
$mgleft = $mgright = $mgtop = $mgbot = 20;
$x0 = 10; $y0 = ($imgh-$mgtop-$mgbot)/2;
$scx = 20;
$scy = 1;
$ngx = 10;
$ngy = 4;

$fp = fopen($imgfile, "w");
if ($fp){
    fputs($fp, "$imgw|$imgh|$mgleft|$mgright|$mgtop|$mgbot|$x0|$y0|$scx|$scy|$ngx|$ngy\r\n");
    fputs($fp, "$DT|$n\r\n");
    fputs($fp, "$u[0]");
    for ($i=1; $i<$n; $i++) {
        fputs($fp, ",$u[$i]");
    }
    fclose($fp);
}
echo "<img src=\"xygraph.php?fname=$imgfile\">";
echo "<table>";
echo "<tr><th>Period</th><td>$Td</td><td>sec</td></tr>";
echo "<tr><th>Dumping ratio</th><td>$zi</td><td></td></tr>";
echo "<tr><th>Max U</th><td>$umax</td><td></td></tr>";
echo "<tr><th>Min U</th><td>$umin</td><td></td></tr>";
echo "<tr><th>Cc</th><td>$Cc</td><td></td></tr>"; 
echo "</table>"; 
?>