tweak parallelism example

examples/more/13_parallelize_min/example.c

@@ -15,7 +15,7 @@ int main()
     // Question being asked: what is the distribution of sampling 1000 times and taking the min?
     double sample_min_of_n(uint64_t* seed, int n){
         double min = sample_normal(5, 2, seed);
-        for(int i=0; i<(n-2); i++){
+        for(int i=0; i<(n-1); i++){
             double sample = sample_normal(5, 2, seed);
             if(sample < min){
                 min = sample;
@@ -27,7 +27,7 @@ int main()
         return sample_min_of_n(seed, 1000);
     } 
 
-    int n_samples = 1000000, n_threads = 16;
+    int n_samples = 10000, n_threads = 16;
     double* results = malloc(n_samples * sizeof(double));
     parallel_sampler(sampler_min_of_1000, results, n_threads, n_samples);
     printf("Mean of the distribution of (taking the min of 1000 samples of a normal(5,2)): %f\n", array_mean(results, n_samples));
@@ -41,27 +41,29 @@ int main()
         int quotient = n / 16;
         int remainder = n % 16;
 
-        uint64_t seed = 1000;
+        uint64_t seed = 100;
         double result_remainder = sample_min_of_n(&seed, remainder);
         
         double sample_min_of_quotient(uint64_t* seed) { 
-            return sample_min_of_n(seed, quotient);
+            double result = sample_min_of_n(seed, quotient);
+            // printf("Result: %f\n", result);
+            return result;
         }
-        double* results_quotient = malloc(quotient * sizeof(double));
-        parallel_sampler(sample_min_of_quotient, results_quotient, n_threads, quotient);
+        double* results = malloc(n_threads * sizeof(double));
+        parallel_sampler(sample_min_of_quotient, results, n_threads, n_threads);
 
-        double min = results_quotient[0];
-        for(int i=1; i<quotient; i++){
-            if(min > results_quotient[i]){
-                min = results_quotient[i];
+        double min = results[0];
+        for(int i=1; i<n_threads; i++){
+            if(min > results[i]){
+                min = results[i];
             }
         }
         if(min > result_remainder){
             min = result_remainder;
         }
-        free(results_quotient);
+        free(results);
         return min;
     }
-    printf("Minimum of 1M samples of normal(5,2): %f\n", sample_n_parallel(1000000));
+    printf("Minimum of 10M samples of normal(5,2): %f\n", sample_n_parallel(1000 * 1000));
 
 }

squiggle_more.c

@@ -326,9 +326,20 @@ void parallel_sampler(double (*sampler)(uint64_t* seed), double* results, int n_
     int divisor_multiple = quotient * n_threads; 
 
     uint64_t** seeds = malloc(n_threads * sizeof(uint64_t*));
+    // printf("UINT64_MAX: %lu\n", UINT64_MAX);
+    srand(1);
     for (uint64_t i = 0; i < n_threads; i++) {
         seeds[i] = malloc(sizeof(uint64_t));
-        *seeds[i] = i + 1; // xorshift can't start with 0
+        // Constraints: 
+        // - xorshift can't start with 0
+        // - the seeds should be reasonably separated and not correlated
+        *seeds[i] = (uint64_t) rand() * (UINT64_MAX / RAND_MAX);
+        // printf("#%ld: %lu\n",i, *seeds[i]);
+
+        // Other initializations tried:
+        // *seeds[i] = 1 + i;
+        // *seeds[i] = (i + 0.5)*(UINT64_MAX/n_threads);
+        // *seeds[i] = (i + 0.5)*(UINT64_MAX/n_threads) + constant * i;
     }
 
     int i;