for sits = 1:stepsize segmentLength = 0.1; if run_RRTconnect == 1 time = 0; avg_its = 0; avg_path = 0; for i = 1:num_of_runs [n_its,path_n,run_time] = RRTconnect_3D(dim,segmentLength,random_world,show_output); time = time + run_time; avg_its = avg_its + n_its; avg_path = avg_path + path_n; end

这段代码中使用了for循环，循环变量为sits，循环次数为stepsize。在循环体内部定义了变量segmentLength的值为0.1，然后判断run_RRTconnect是否等于1，如果是，则定义变量time、avg_its和avg_path的值都为0，接着再使用for循环，循环变量为i，循环次数为num_of_runs。在循环体内部调用了函数RRTconnect_3D，并将返回值分别赋值给变量n_its、path_n和run_time。然后累加变量time、avg_its和avg_path的值。最后，在循环体外部结束了for循环sits，并且此时变量time、avg_its和avg_path的值都是所有循环的累加值。

相关问题

class MyCar: steer_shape='rectangle' __weight=3000 def init(self,n_wheel,n_sits): self.n_wheel=n_wheel self.n_sits=n_sits def run(self): print("The car has already started") print(MyCar.dict) print(MyCar._MyCar__weight) mycar=MyCar(4,5) mycar.run() 在上例基础上，通过mycar采用两种不同方法访问属性 n_wheel

可以通过以下两种方法访问属性 n_wheel：

1. 直接使用实例对象 mycar.n_wheel，如下所示：

print(mycar.n_wheel)

2. 使用类对象 MyCar 和属性名 n_wheel，通过类访问实例属性，如下所示：

print(MyCar.n_wheel.__get__(mycar))

这两种方法都可以访问到实例属性 n_wheel 的值。

The Sleeping Teaching Assistant A university computer science department has a teaching assistant (TA) who helps undergraduate students with their programming assignments during regular office hours. The TA’s office is rather small and has room for only one desk with a chair and computer. There are three chairs in the hallway outside the office where students can sit and wait if the TA is currently helping another student. When there are no students who need help during office hours, the TA sits at the desk and takes a nap. If a student arrives during office hours and finds the TA sleeping, the student must awaken the TA to ask for help. If a student arrives and finds the TA currently helping another student, the student sits on one of the chairs in the hallway and waits. If no chairs are available, the student will come back at a later time. Using POSIX threads, mutex locks, and/or semaphores, implement a solution that coordinates the activities of the TA and the students. Details for this assignment are provided below. Using Pthreads, begin by creating N students. Each will run as a separate thread. The TA will run as a separate thread as well. Student threads will alternate between programming for a period of time and seeking help from the TA. If the TA is available, they will obtain help. Otherwise, they will either sit in a chair in the hallway or, if no chairs are available, will resume programming and will seek help at a later time. If a student arrives and notices that the TA is sleeping, the student must notify the TA using a semaphore. When the TA finishes helping a student, the TA must check to see if there are students waiting for help in the hallway. If so, the TA must help each of these students in turn. If no students are present, the TA may return to napping. Perhaps the best option for simulating students programming—as well as the TA providing help to a student—is to have the appropriate threads sleep for a random period of time using the sleep() API:

This is a programming assignment that requires the use of POSIX threads, mutex locks, and/or semaphores to coordinate the activities of the TA and the students. Here is one possible solution:

1. Create a mutex lock and two semaphores: one for the TA and one for the students waiting in the hallway.
2. Create N student threads and one TA thread.
3. Each student thread should loop indefinitely, alternating between programming and seeking help from the TA.
4. When a student needs help, they should try to acquire the mutex lock. If the TA is sleeping, the student should signal the TA semaphore and wait on the student semaphore. If the TA is helping another student, the student should wait on the student semaphore.
5. When the TA wakes up, they should try to acquire the mutex lock. If there are students waiting in the hallway, the TA should signal the student semaphore N times to wake up the students. The TA should then help each student in turn, releasing the mutex lock after each one is helped.
6. If there are no students waiting, the TA should release the mutex lock and go back to sleep.

Here is some sample code to implement this solution:

#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define N 10 // number of students
#define CHAIRS 3 // number of chairs in hallway

pthread_t students[N], ta;
pthread_mutex_t mutex;
sem_t student_sem, ta_sem;

int waiting = 0;

void *student(void *arg) {
    int id = *(int*)arg;
    while (1) {
        // program for a random amount of time
        sleep(rand() % 10 + 1);
        printf("Student %d needs help\n", id);
        pthread_mutex_lock(&mutex);
        if (waiting < CHAIRS) {
            // there is a free chair in the hallway
            waiting++;
            printf("Student %d waiting in hallway (%d/%d)\n", id, waiting, CHAIRS);
            pthread_mutex_unlock(&mutex);
            sem_wait(&student_sem);
            waiting--;
        } else {
            // no free chairs in the hallway
            printf("Student %d will come back later\n", id);
            pthread_mutex_unlock(&mutex);
        }
        // get help from TA
        printf("Student %d getting help from TA\n", id);
        // help for a random amount of time
        sleep(rand() % 5 + 1);
    }
}

void *ta_helper(void *arg) {
    while (1) {
        // sleep until a student wakes us up
        sem_wait(&ta_sem);
        while (1) {
            pthread_mutex_lock(&mutex);
            if (waiting == 0) {
                // no students waiting, go back to sleep
                pthread_mutex_unlock(&mutex);
                break;
            }
            // help the next student in line
            waiting--;
            sem_post(&student_sem);
            printf("TA helping a student (%d/%d)\n", waiting, CHAIRS);
            pthread_mutex_unlock(&mutex);
            // help for a random amount of time
            sleep(rand() % 5 + 1);
        }
    }
}

int main() {
    // initialize mutex lock and semaphores
    pthread_mutex_init(&mutex, NULL);
    sem_init(&student_sem, 0, 0);
    sem_init(&ta_sem, 0, 0);
    // create student threads
    int student_ids[N];
    for (int i = 0; i < N; i++) {
        student_ids[i] = i;
        pthread_create(&students[i], NULL, student, &student_ids[i]);
    }
    // create TA thread
    pthread_create(&ta, NULL, ta_helper, NULL);
    // wait for threads to finish
    for (int i = 0; i < N; i++) {
        pthread_join(students[i], NULL);
    }
    pthread_join(ta, NULL);
    // clean up mutex lock and semaphores
    pthread_mutex_destroy(&mutex);
    sem_destroy(&student_sem);
    sem_destroy(&ta_sem);
    return 0;
}

Note that this is just one possible solution and there may be other ways to implement the same behavior using different synchronization primitives.