找到 y 最小的 x

Question

I have a polynomial in a range (-2,2) . I can easily find min y values by iterating with x=0.1 . But I also want to find corresponding x value where y is minimum. (without using any additional libraries)

Let's say y=x**2+3*x+5. I want to find min(y) in a range(-2,2) and also want to find x which gives min(y).

def f(x):
   return x**2+3*x+5
y=[]
x=[i/10 for i in range(-20,20)]
for x in x:
   y_values.append(f1(x))

#min(y) find also minimum of y but I want to find it with long way.

   minimum1=y_values[0]
   for n in y_values: 
        if minimum1>n:
           minimum1=n

Answer 1

Since tuples are ordered by the first items and then the second items and so on, you can pass to the min function a generator expression that outputs tuples of (y, x) :

min((f(x), x) for x in (i / 10 for i in range(-20, 20)))

This returns:

(2.75, -1.5)

Answer 2

Maybe just doing the comparison at the same time you call the function?

def f(x):
   return x**2+3*x+5

y=[]
x=[i/10 for i in range(-20,20)]

ymin = f1(x[0])
xmin = x[0]

for x in x:
   if(f1(x)<y):
       ymin = f1(x)
       xmin = x
   y_values.append(f1(x))