php中数组赋值混乱求解

$update=['f1'=>121.231,'f2'=>2312.12,     'f3'=>31.1231,'f4'=>213.12,'fv'=>3189.21321];$month=['m1'=>123.1289,'m2'=>123.23198,      'm3'=>23.21,'m4'=>138.21,'mv'=>1231.81];		foreach($update as &$v){			$v=round($v,4);		}		foreach($month as $k=>$v){			$update[$k]=round($v,4);		}

		if($debug_flag){			echo('原始数据');BR();			PR($update);		}		foreach($update as $k=>&$v){			$v=round($v,4);		}		//实在没有整明白为什么update的最后一个fv不进行四舍五入呢？		if($debug_flag){			echo('update foreach 循环后数据');BR();			PR($update);			echo('进入month循环');BR();			echo('month原始数据');BR();			PR($month);		}		foreach($month as $k=>$v){			if($debug_flag){				echo('in month ');BR();				PR($update);				PR($k);BR();			}			$update[$k]=round($v,4);			if($debug_flag){				PR($update);				echo('month 循环中数据');BR();			}		}		if($debug_flag){			echo('month循环后数据');BR();			PR($update);			PR($month);			die();		}

原始数据Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.85900353103)update foreach 循环后数据Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.859)进入month循环month原始数据Array(    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825    [mv] => 600.85900353103)in monthArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 0)m0Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 0    [m0] => 0)month 循环中数据in monthArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 596.4    [m0] => 0)m1Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 596.4    [m0] => 0    [m1] => 596.4)month 循环中数据in monthArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 604.5    [m0] => 0    [m1] => 596.4)m2Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 604.5    [m0] => 0    [m1] => 596.4    [m2] => 604.5)month 循环中数据in monthArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.3325    [m0] => 0    [m1] => 596.4    [m2] => 604.5)m3Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.3325    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325)month 循环中数据in monthArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 602.0825    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325)m4Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 602.0825    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825)month 循环中数据in monthArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.85900353103    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825)mvArray(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.85900353103    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825    [mv] => 600.859)month 循环中数据month循环后数据Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.85900353103    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825    [mv] => 600.859)Array(    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825    [mv] => 600.85900353103)

		$update=array_merge($update,$month,$year);		foreach($update as &$v){			$v=round($v,4);		}

$update = array (  'f1' => 596.4,  'f2' => 604.5,  'f3' => 600.3325,  'f4' => 602.0825,  'fv' => 600.85900353103,);$month = array (  'm0' => 0,  'm1' => 596.4,  'm2' => 604.5,  'm3' => 600.3325,  'm4' => 602.0825,  'mv' => 600.85900353103,);foreach($update as $k=>&$v){    $v = round($v, 4);}unset($v);foreach($month as $k=>$v){    $update[$k] = round($v, 4);}print_r($update);

Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.859    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825    [mv] => 600.859)

$update = array (  'f1' => 596.4,  'f2' => 604.5,  'f3' => 600.3325,  'f4' => 602.0825,  'fv' => 600.85900353103,);$month = array (  'm0' => 0,  'm1' => 596.4,  'm2' => 604.5,  'm3' => 600.3325,  'm4' => 602.0825,  'mv' => 600.85900353103,);foreach($update as $k=>&$v){    $v = round($v, 4);}unset($v);foreach($month as $k=>$v){    $update[$k] = round($v, 4);}print_r($update);

Array(    [f1] => 596.4    [f2] => 604.5    [f3] => 600.3325    [f4] => 602.0825    [fv] => 600.859    [m0] => 0    [m1] => 596.4    [m2] => 604.5    [m3] => 600.3325    [m4] => 602.0825    [mv] => 600.859)