blocks|key|412774|text|您的猜测是对的:代码正在尝试立即计算x**3%2B2*x-4。不幸的是，你不能真正阻止它这样做。好消息是，在Python中，函数是一级对象，我的意思是，您可以像对待任何其他变量一样对待它们。因此，要修复您的函数，我们可以这样做：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|412775|import+numpy+as+np++
import+matplotlib.pyplot+as+plt++

def+graph(formula,+x_range):++
++++x+=+np.array(x_range)++
++++y+=+formula(x)++#+<-+note+now+we're+calling+the+function+'formula'+with+x
++++plt.plot(x,+y)++
++++plt.show()++

def+my_formula(x):
++++return+x**3%2B2*x-4

graph(my_formula,+range(-10,+11))|code-block|syntax|javascript|412776|如果您想在一行中完成所有这些工作，您可以使用所谓的lambda函数，它只是一个没有名称的简短函数，其中您不使用def或return|412777|graph(lambda+x:+x**3%2B2*x-4,+range(-10,+11))|412778|您可以查看np.arange+(它允许非整数增量)和np.linspace，它允许您指定开始、停止和要使用的点数，而不是range。|412779|entityMap^0|I|A|0|0|P|6|1J|3|1N|6|0|0|5|9|Q|B|1O|5|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|R|$]]

Your guess is right: the code is trying to evaluate <code>x**3+2*x-4</code> immediately. Unfortunately you can't really prevent it from doing so. The good news is that in Python, functions are first-class objects, by which I mean that you can treat them like any other variable. So to fix your function, we could do:

<pre><code>import numpy as np 
import matplotlib.pyplot as plt 

def graph(formula, x_range): 
 x = np.array(x_range) 
 y = formula(x) # &lt;- note now we're calling the function 'formula' with x
 plt.plot(x, y) 
 plt.show() 

def my_formula(x):
 return x**3+2*x-4

graph(my_formula, range(-10, 11))
</code></pre>

If you wanted to do it all in one line, you could use what's called a <code>lambda</code> function, which is just a short function without a name where you don't use <code>def</code> or <code>return</code>:

<pre><code>graph(lambda x: x**3+2*x-4, range(-10, 11))
</code></pre>

And instead of <code>range</code>, you can look at <code>np.arange</code> (which allows for non-integer increments), and <code>np.linspace</code>, which allows you to specify the start, stop, and the number of points to use.

blocks|key|194708|text|这是因为在队列中|type|unstyled|depth|inlineStyleRanges|entityRanges|data|194709|graph(x**3%2B2*x-4,+range(-10,+11))|code-block|syntax|javascript|194710|未定义X。|194711|最简单的方法是将想要绘制的函数作为字符串传递，并使用eval将其作为表达式进行计算。|offset|length|style|CODE|194712|因此，您的代码只需进行最少的修改即可|194713|import+numpy+as+np++
import+matplotlib.pyplot+as+plt++
def+graph(formula,+x_range):++
++++x+=+np.array(x_range)++
++++y+=+eval(formula)
++++plt.plot(x,+y)++
++++plt.show()|194714|你可以这样叫它|194715|graph('x**3%2B2*x-4',+range(-10,+11))|194716|entityMap^0|0|0|0|Q|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@$K|12|L|13|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|14|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|16|8|@]|9|@]|A|$]]|$1|U|3|V|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

This is because in line 

<pre><code>graph(x**3+2*x-4, range(-10, 11))
</code></pre>

x is not defined. 

The easiest way is to pass the function you want to plot as a string and use <code>eval</code> to evaluate it as an expression. 

So your code with minimal modifications will be 

<pre><code>import numpy as np 
import matplotlib.pyplot as plt 
def graph(formula, x_range): 
 x = np.array(x_range) 
 y = eval(formula)
 plt.plot(x, y) 
 plt.show()
</code></pre>

and you can call it as 

<pre><code>graph('x**3+2*x-4', range(-10, 11))
</code></pre>

blocks|key|412869|text|要绘制未针对特定变量(如圆或双曲线)求解的方程：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|412870|import+numpy+as+np++
import+matplotlib.pyplot+as+plt++
plt.figure()+#+Create+a+new+figure+window
xlist+=+np.linspace(-2.0,+2.0,+100)+#+Create+1-D+arrays+for+x,y+dimensions
ylist+=+np.linspace(-2.0,+2.0,+100)+
X,Y+=+np.meshgrid(xlist,+ylist)+#+Create+2-D+grid+xlist,ylist+values
F+=+X**2+%2B+Y**2+-+1++#++'Circle+Equation
plt.contour(X,+Y,+F,+[0],+colors+=+'k',+linestyles+=+'solid')
plt.show()|code-block|syntax|javascript|412871|更多信息：http://courses.csail.mit.edu/6.867/wiki/images/3/3f/Plot-python.pdf|offset|length|412872|entityMap|0|LINK|mutability|MUTABLE|url|http://courses.csail.mit.edu/6.867/wiki/images/3/3f/Plot-python.pdf^0|0|0|5|1V|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

To plot an equation that is not solved for a specific variable (like circle or hyperbola):

<pre><code>import numpy as np 
import matplotlib.pyplot as plt 
plt.figure() # Create a new figure window
xlist = np.linspace(-2.0, 2.0, 100) # Create 1-D arrays for x,y dimensions
ylist = np.linspace(-2.0, 2.0, 100) 
X,Y = np.meshgrid(xlist, ylist) # Create 2-D grid xlist,ylist values
F = X**2 + Y**2 - 1 # 'Circle Equation
plt.contour(X, Y, F, [0], colors = 'k', linestyles = 'solid')
plt.show()
</code></pre>

More about it: <a href="http://courses.csail.mit.edu/6.867/wiki/images/3/3f/Plot-python.pdf" rel="noreferrer">http://courses.csail.mit.edu/6.867/wiki/images/3/3f/Plot-python.pdf</a>

I'm trying to make a function that will graph whatever formula I tell it to.

<pre><code>import numpy as np 
import matplotlib.pyplot as plt 
def graph(formula, x_range): 
 x = np.array(x_range) 
 y = formula 
 plt.plot(x, y) 
 plt.show() 
</code></pre>

When I try to call it the following error happens, I believe it's trying to do the multiplication before it gets to <code>y = formula</code>. 

<pre><code>graph(x**3+2*x-4, range(-10, 11))

Traceback (most recent call last): 
 File "&lt;pyshell#23&gt;", line 1, in &lt;module&gt; 
 graph(x**3+2*x-4, range(-10, 11)) 
NameError: name 'x' is not defined 
</code></pre>

graphing an equation with matplotlib

Python

我正在尝试创建一个函数，它将为我告诉它的任何公式绘制图形。import numpy as np  import matplotlib.pyplot as plt  def graph(formula, x_range):      x = np.array(x_range)      y = formula      ...

问用matplotlib绘制方程式
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