Is this test tautological?

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.