我将信号的相位从0度改变为360度，以获得最大电压值。因为如果我改变信号的相位，电压也会发生变化。我有以下代码来找到最大值。
void Maxphase(float *max, unsigned int *index)
{
*max = 0.0;
float value;
unsigned int i, data;
for (i=0;i<=360;i++)
{
phaseset(i);
delay_ms(100);
data = readvalue();
value = voltage(mux1);
if(value > *max) //find max value
{
*max = value; //max voltage
*index = i;
}
}
}
从上面的代码我得到38秒（360 * 100）后的最大值（电压），因为对于每次读取操作，我的设备需要100ms延迟。这太大了，我无法改变硬件因此我希望通过优化软件在2到3秒内获得最大值。 然后我尝试了以下的代码。
void Maxphase(float *max1, unsigned int *index1)
{
max = 0.0;
float value;
unsigned int i,j,data;
for (i=0;i<=360;i+=10)
{
phaseset(i);
delay_ms(100);
data = readvalue();
value = voltage(mux1);
if(value > max) //find max value
{
max = value; //max voltage
index = i;
}
}
*max1=max;
*index1=index;
for (i=*index1-9;i<=*index1+9;i+=1)
{
j=i;
phaseset(j);
delay_ms(100);
data = readvalue();
value = voltage(mux1);
if(value > *max1) //find max value
{
*max1 = value; //max voltage
*index1 = i;
}
}
}
我将时间从45秒减少到7秒。我将迭代次数减少到了360到54（54 * 100）。我希望将其缩短7秒到2秒。
任何人都可以用更好的算法帮助我，我可以在2秒内从（0到360）获得最大值。
我通过改变相位使用示波器测量了电压值。我在下面写了它如何随相位变化电压。
Phase (degree) voltage(max)
0 0.9mv
45 9.5mv
90 9.0mv
135 0.9mv
180 292mv
225 601mv
270 555mv
315 230mv
360 0.9mv
我是C编程新手。任何人都可以提供最佳算法的示例代码。
答案 0 :(得分：2)
Golden section search可能就是你所追求的。它很有效，但仍然很简单。
如果您想要更快更复杂的东西，可以使用Brent's method。
答案 1 :(得分：1)
如果你可以确定360度只有一个最高点你可以做一个递归的分裂和征服。
你首先看看，例如在0,180,270。让我们说你发现答案是180 + 270一起具有最高值。比你从210开始看......哪一方更高？等等...
答案 2 :(得分：0)
在这里利用各种意见和建议，我提出了这个未经测试的代码。我不知道这是否有效或者是对现有资源的改进，但无论如何尝试都很有趣：
extern void phaseset(int);
extern void delay_ms(int);
extern float readvalue();
extern float voltage(int);
extern int mux1;
float probe(int phase)
{
float data;
phaseset(phase);
delay_ms(100);
data = readvalue(); /* data is ignored? */
return voltage(mux1); /* mux1? */
}
/* helper routine, find the max in a given range [phase1, phase2] */
void maxphase_aux(int phase1, float vol1, int phase2, float vol2, int *phaseret, float *volret)
{
float xvol1 = 0, xvol2 = 0;
int xphase1 = -1, xphase2 = -1;
/* test the voltage in the middle */
int phasem = abs(phase2 - phase1) / 2;
float volm = probe(phasem);
if (volm > vol1 && volm > vol2) {
/* middle point is the highest so far,
* search left and right for maximum */
*volret = volm;
*phaseret = phasem;
maxphase_aux(phase1, vol1, phasem, volm, &xphase1, &xvol1);
maxphase_aux(phase2, vol2, phasem, volm, &xphase2, &xvol2);
} else if (volm < vol1 && volm > vol2) {
/* vol1 is the highest so far,
* search between volm and vol1 for maximum */
maxphase_aux(phase1, vol1, phasem, volm, &xphase1, &xvol1);
} else if (volm > vol1 && volm < vol2) {
/* vol2 is the highest so far,
* search between volm and vol2 for maximum */
maxphase_aux(phase2, vol2, phasem, volm, &xphase2, &xvol2);
} else {
/* not possible? */
return;
}
if (xvol1 > volm) {
*volret = xvol1;
*phaseret = xphase1;
}
if (xvol2 > volm) {
*volret = xvol2;
*phaseret = xphase2;
}
}
void maxphase(int *phaseret, float *volret)
{
float v0 = probe(0);
float v360 = probe(360);
maxphase_aux(0, v0, 360, v360, phaseret, volret);
}
答案 3 :(得分：0)
更新时间：2012-11-10。
#include <stdio.h>
#include <string.h>
#include <math.h>
#define FAKE_TARGET 89
unsigned fake_target = FAKE_TARGET;
float probe_one(unsigned int phase);
void Maxphase(float *max, unsigned int *index);
void Maxphase(float *max, unsigned int *index)
{
unsigned int aim, idx, victim;
struct best {
unsigned pos;
float val;
} samples[4] = {{0, 0.0}, };
for (aim = 0;aim < 360;aim += 90) {
idx=aim/90;
samples[idx].pos = aim;
samples[idx].val = probe_one(samples[idx].pos);
if (!idx || samples[idx].val < samples[victim].val ) victim = idx;
}
/* eliminate the weakist postion, and rotate the rest,
** such that:
** samples[0] := lower boundary.
** samples[1] := our best guess
** samples[2] := upper boundary
** samples[3] := scratch/probe element
*/
fprintf(stderr, "Victim=%u\n", victim );
switch(victim) {
case 0: samples[0] = samples[1]; samples[1] = samples[2]; samples[2] = samples[3]; break;
case 1: samples[1] = samples[3]; samples[3] = samples[0]; samples[0] = samples[2]; samples[2] = samples[3]; break;
case 2: samples[2] = samples[1]; samples[1] = samples[0]; samples[0] = samples[3]; break;
case 3: break;
}
/* Calculation is easier if the positions are increasing.
** (We can always perform the modulo 360 if needed)
*/
if (samples[0].pos > samples[1].pos ) samples[1].pos += 360;
if (samples[1].pos > samples[2].pos ) samples[2].pos += 360;
while( 1) {
int step;
step = samples[2].pos - samples[0].pos;
if (step < 3) break;
do {
fprintf(stderr, "\n[%u %u %u] Diff=%d\n"
, samples[0].pos , samples[1].pos , samples[2].pos , step);
if (step > 0) step++; else step--;
step /= 2;
aim = (samples[0].pos + step ) ;
/* avoid hitting the middle cell twice */
if (aim %360 != samples[1].pos %360) break;
step += 1;
aim = (samples[0].pos + step ) ;
if (aim %360 != samples[1].pos %360) break;
step -= 2;
aim = (samples[0].pos + step ) ;
break;
} while(0);
fprintf(stderr, "Step=%d Aim=%u, Idx=%u\n",step, aim,idx );
samples[3].pos = aim;
samples[3].val = probe_one( samples[3].pos );
victim= (samples[3].pos > samples[1].pos ) ? 2 : 0;
if (samples[3].val > samples[1].val) idx= 1; else idx = victim;
fprintf(stderr, "Victim=%u, TargetIdx=%u\n", victim, idx );
/* This should not happen */
if (samples[3].val < samples[victim].val) break;
if (idx != victim) samples[2-victim] = samples[idx];
samples[idx] = samples[3];
}
*max = samples[1].val;
*index = samples[1].pos % 360;
}
float probe_one(unsigned int phase)
{
float value;
#ifdef FAKE_TARGET
int dif;
dif = fake_target-phase;
if (dif < -180) dif = 360+dif;
else if (dif > 180) dif = 360-dif;
/* value = 1.0 / (1 + pow(phase-231, 2)); */
value = 1.0 / (1 + pow(dif, 2));
fprintf(stderr, "Target = %d: Probe(%d:%d) := %f\n", fake_target, phase, dif, value );
sleep (1);
#else
unsigned int data;
phase %= 360;
phaseset(phase);
delay_ms(100);
data = readvalue(); // what is this ?
value = voltage(mux1);
#endif
return value;
}
int main(int argc, char **argv)
{
float value;
unsigned int index;
if (argv[1]) sscanf (argv[1], "%u", &fake_target);
fake_target %= 360;
Maxphase(&value, &index) ;
printf("Phase=%u Max=%f\n", index, value );
return 0;
}