Lære Functions of Several Variables

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When you first encounter functions of several variables, you are expanding the idea of a function from single input–output relationships to situations where the output depends on two or more inputs. In mathematics, a function of several variables is a rule that assigns a single output value to each combination of input values. For example, a function $f(x, y)$ takes two inputs, $x$ and $y$ , and produces one output. This is written as $f: R^2 → R$ , which means the function's domain is the set of all ordered pairs of real numbers, and its range is the set of real numbers.

You see functions of several variables everywhere in real life. The temperature at a point on Earth's surface depends on both latitude and longitude, so it is a function of two variables. The profit a company makes might depend on both the price of its product and the amount spent on advertising, again making it a function of two variables. If you add a third variable, such as time, you get a function of three variables: $f(x, y, t)$ .

The domain of a multivariate function is the set of all input values for which the function is defined. The range is the set of all possible output values. For a function $f(x, y)$ , the domain might be all pairs $(x, y)$ in a certain region of the plane, and the range would be all real numbers that $f(x, y)$ can produce as those pairs vary within the domain.

To interpret these functions, you often visualize them. For functions of two variables, you can plot the output as a surface above the $xy$ -plane, or you can use contour lines to show where the function has the same value. This helps you see how the function behaves as you change the inputs.


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import numpy as np
import matplotlib.pyplot as plt

# Define a simple function of two variables: f(x, y) = x^2 + y^2
def f(x, y):
    return x**2 + y**2

# Create a grid of x and y values
x = np.linspace(-3, 3, 50)
y = np.linspace(-3, 3, 50)
X, Y = np.meshgrid(x, y)
Z = f(X, Y)

# Plot the surface
fig = plt.figure(figsize=(8, 6))
ax = fig.add_subplot(111, projection='3d')
ax.plot_surface(X, Y, Z, cmap='viridis', alpha=0.8)
ax.set_xlabel('x')
ax.set_ylabel('y')
ax.set_zlabel('f(x, y)')
ax.set_title('Surface plot of f(x, y) = x^2 + y^2')

plt.show()

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