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main.cc
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Mon, Feb 24, 01:49

main.cc
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/* -------------------------------------------------------------------------- */
#include <cstdlib>
#include <cmath>
#include <iostream>
/* -------------------------------------------------------------------------- */
void ex1(){
std::cout << "EXERCISE 1" << std::endl;
int a = 0.5;
std::cout << a << std::endl;
// conversion from double to int
double a2 = 1/2;
std::cout << a2 << std::endl;
// Using int variables to "make it double"
// It does not happen in python because of dynamic typing.
}
double tanhx(double x){
return (exp(x) - exp(-x)) / (exp(x) + exp(-x));
}
double tanhx2(double x){
return (1 - exp(-2 * x)) / (1 + exp(-2 * x));
}
double tanhx3(double x){
return (2 * exp(-2 * x)) / (1 + exp(-2 * x));
}
void ex2(){
std::cout << "EXERCISE 2" << std::endl;
double x = 10.;
double a = exp(x);
std::cout << "x = " << x << ", exp(x) = " << a << std::endl;
for (double x = 0; x< 1000; x += 100){
std::cout << "x = " << x <<
": tanh(x) = " << tanhx(x) <<
", tanhx2(x) = " << tanhx2(x) <<
", tanhx3(x) = " << tanhx3(x) << std::endl;
}
}
double evolution(double pn, double v, double dt){
return (pn + dt *v);
}
void ex3(){
std::cout << "EXERCISE 3" << std::endl;
double v = 3e8;
double p0 = 0;
double p1 = 1e-3;
double dt = 1000;
for (int i = 0; i < 40; i++){
p0 = evolution(p0, v, dt);
p1 = evolution(p1, v, dt);
std::cout << "Cycle " << i <<
": P0 = " << p0 << ", P1 = " << p1 <<
", distance = " << p1 - p0 << std::endl;
}
// Initially, p0 and p1 are very small numbers hence the computer can
// compute their distance accurately.
// As the photons evolve, p0 and p1 become very big, the subtraction p1 - p0
// loses information about their smallest decimals, hence their distance
// is approximated as zero.
}
int main(int argc, char ** argv){
int n = 0;
if (argc > 1) {
n = atoi(argv[1]);
}
switch (n) {
case 0:
ex1();
ex2();
ex3();
break;
case 1:
ex1();
break;
case 2:
ex2();
break;
case 3:
ex3();
break;
default:
std::cout << "Unkown exercise ID: " << n << std::endl;
}
return EXIT_SUCCESS;
}

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