Question

我想研究python中的符号函数。我想创建y(x) = x^2 + 2x + 3并将其绘制在[1, 255]范围内。我想使用subs()函数通过使用for循环来计算值。但是，当我运行该命令时，出现此错误：

IndexError('list index out of range')

你能帮我吗？

import numpy as np
import matplotlib.pyplot as plot
from sympy import *

a = [1,2,3]

x = Symbol('x')
fx = a[0]*x**2 + a[1]*x + a[2]

t = list(range(1,256))
y = np.zeros(256)

for i in t:
    y[i] = fx.subs({x:t[i]})

plot.plot(t,y)
plot.show()

Answer 1

只需替换为以下行：

import { Component, OnInit } from '@angular/core';
import { Observable, from, of, GroupedObservable } from 'rxjs';
import { distinct, map, mergeMap, toArray, groupBy } from 'rxjs/operators';

export class ModelA {
  id: number;
  name: string;
}

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent implements OnInit {
  name = 'Angular';

  models: Observable<ModelA[]>;
  distinctModels: Observable<ModelA[]>;
  groupedModels: Observable<ModelA[][]>;

  ngOnInit() {
    this.loadData();
  }

  loadData(): void {
    this.models = of([
      {id: 1, name: 'Name A'},
      {id: 2, name: 'Name A'},
      {id: 3, name: 'Name B'},
      {id: 4, name: 'Name C'}
    ]);

    this.distinctModels = this.models
        .pipe(
          mergeMap(models => models),
          distinct(m => m.name),
          toArray()
        );
    this.distinctModels.subscribe( m => console.log(m));

    this.groupedModels = this.models
        .pipe(
          mergeMap(models =>models),
          groupBy(model => model.name),
          mergeMap(toArray()),
          toArray()
        );
    this.groupedModels.subscribe( m => console.log(m));
  }
}

问题在于代码中y = np.zeros(len(t)) for i in range(len(t)): y[i] = fx.subs({x:t[i]})的长度仅为t，而255的长度为y，因为您定义了256，因此y = np.zeros(256)，因为没有Index Error。我使用t[256]是因为您的y = np.zeros(len(t))点与y（或t）点一样多。顺便说一句，由于调用x，极有可能在当前的绘图命令中出现错误。我将其简称为import matplotlib.pyplot as plot而不是plt

输出

I made a sample project

如何在Python中将值数组插入符号函数

1 个答案: