Is this test tautological? - c++

Question

Given some
double x;
what is the difference between
if((x>0 || (x<=0)))
and if(true)? Is there any difference? I think they are equivalent, but it seems it's not the case? Anybody knows why?
Ok, I am new to cpp and I am sorry for this question. But I truly need to solve this problem
double sigmaX = 0.1;
double sigmaY = 0.1;
SimPFilter::SimPFilter() {
totalParticles = 100;
nFilters = 2;
gsl_rng_env_setup();
rng = gsl_rng_alloc(gsl_rng_mt19937);
gsl_rng_set(rng, time(NULL));
}
SimPFilter::~SimPFilter() {
}
void SimPFilter::initParticles(double initX, gsl_rng* rng){
for (int i=0; i < totalParticles; i++) {
particles[i].xp = particles[i].x = 0.5 + gsl_ran_gaussian(rng, sigmaX*sigmaX);
if(i > totalParticles/2)
particles[i].xp = particles[i].x = -0.5 + gsl_ran_gaussian(rng, sigmaX*sigmaX);
particles[i].wNormalized = 1/(totalParticles/nFilters);
int j = (int)i/(totalParticles/nFilters);
particles[i].id = j;
filters[j].nParticles = (totalParticles/nFilters);
particles[i].w = particles[i].wp = particles[i].wNormalized = 1/totalParticles;
}
for(int i =0; i<nFilters; i++){
filters[i].weight = filters[i].weightPrev = 1.0/nFilters;
}
}
void SimPFilter::transition(gsl_rng* rng){
for (int i=0; i < totalParticles; i++) {
double temp = particles[i].x;
particles[i].xp = temp;
particles[i].x += gsl_ran_gaussian(rng, sigmaX*sigmaX); //the centre of each region
}
}
double SimPFilter::measure_prob(particle *p, double obser_y, gsl_rng* rng){
double x = p->x;
//cout << "x value is " << x << endl;
double prob = gsl_ran_gaussian_pdf (obser_y - (x*x), sigmaY);
//cout << "probability " << prob << endl;
std::cout << std::boolalpha;
//cout << (x>0 || (x<=0)) << endl;
if(true){
//cout << "probability2 " << prob << endl;
return prob;
}
return prob;
}
void SimPFilter::updateWeight(double obser_y, gsl_rng* rng){
for (int i=0; i < totalParticles; i++) {
double temp = particles[i].w;
particles[i].wp = particles[i].w;
particles[i].w = measure_prob(&particles[i], obser_y, rng);
}
//normalized particle weight
double eachFilterSum[nFilters];
for(int i=0; i < totalParticles; i++){
int id = particles[i].id;
eachFilterSum[id] += particles[i].w;
}
for(int i=0; i < totalParticles; i++){
particles[i].wNormalized = particles[i].w / eachFilterSum[particles[i].id];
}
//update each filter's weight
double eachFilterW[nFilters];
for(int i=0; i< totalParticles; i++){
//cout << "prticle i's weight1 "<<particles[i].w << endl;
int id = particles[i].id;
eachFilterW[id] += particles[i].wNormalized;
}
double sigmaweight =0; // simga pi n t-1 * wnt
for(int j=0; j<nFilters; j++){
sigmaweight += filters[j].weightPrev * eachFilterW[j];
}
for(int j=0; j<nFilters; j++){
double temp = filters[j].weight;
filters[j].weight = filters[j].weightPrev * eachFilterW[j] / sigmaweight;
filters[j].weightPrev = temp;
}
}
void SimPFilter::resample(gsl_rng* rng){
particle * newParticles;
newParticles = (particle*) malloc(totalParticles * sizeof(particle));
int index =(int)gsl_rng_uniform (rng)* totalParticles;
double beta = 0.0;
double maxWeight =0;
for (int i=0; i < totalParticles; i++) {
maxWeight = max(maxWeight, particles[i].wNormalized* filters[particles[i].id].weight);
}
for(int j=0; j < totalParticles; j++){
beta += (rng, 0, 2*maxWeight);
while(beta > particles[index].wNormalized * (filters[particles[index].id].weight)){
beta -= particles[index].wNormalized * (filters[particles[index].id].weight);
index = (index+1) % totalParticles;
}
newParticles[j] = particles[index];
}
for(int i=0; i<totalParticles; i++){
particles[i] = newParticles[i];
particles[i].w = particles[i].wNormalized = particles[i].wp =1/filters[particles[i].id].nParticles;
}
//update each filter particles number
vector<int> countP;
for(int i=0; i<nFilters; i++){
countP.push_back(0);
}
for(int i=0; i< totalParticles; i++){
countP.at(particles[i].id)++;
}
for(int i=0; i< nFilters; i++){
filters[i].nParticles = countP.at(i);
}
for(int i=0; i< nFilters;i++)
cout << "n particle value is " << filters[i].nParticles << endl;
free(newParticles);
}
`
in the measure_prob function, I find out, if(true) or if(x>=0 || x<0) give different result. When if(true) it could track two objects, but when I use if(x>=0 || x<0) it will converge to one object quickly. I am really confused...

Answer 1

Example :
double x = log2(-1); // Evaluates to NAN
if (x>0 || (x<=0)) {
printf("True\n");
}
else {
printf("False\n");
}
OUTPUT
False
Hence they are not equivalent. NAN stands for Not A Number so it is neither greater than 0 nor is it equal to or less than zero cause it is not a number.