Free Field Operator: Building Quantum Fields

Free Field Operator: Building Quantum Fields How Quantum Fields Evolve Without Interactions ๐ŸŽฏ Our Goal We aim to construct the free scalar field operator \( A(x,t) \), which describes a quantum field with no interactions—just free particles moving across space-time. ๐Ÿง  Starting Expression This is the mathematical formula for our field \( A(x,t) \): \[ A(x, t) = \frac{1}{(2\pi)^{3/2}} \int_{\mathbb{R}^3} \frac{1}{\sqrt{k_0}} \left[ e^{i(k \cdot x - k_0 t)} a(k) + e^{-i(k \cdot x - k_0 t)} a^\dagger(k) \right] \, dk \] x: Spatial position t: Time k: Momentum vector k₀ = √(k² + m²): Relativistic energy of the particle a(k): Operator that removes a particle (annihilation) a†(k): Operator that adds a particle (creation) ๐Ÿงฉ What Does This Mean? The field is made up of wave patterns (Fourier modes) linked to momentum \( k \). It behaves like a system that decides when and where ...

Navigating SageMath’s Interface: Deep Dive with Examples

Meta Description: 

Explore more examples to master the SageMath interface. Dive deeper into calculations, graphing, interactive features, and customizations in this advanced walkthrough.

๐Ÿ”„ A Quick Recap

Previously, we explored how to launch SageMath, navigate its interface, and perform basic calculations. In this post, we’ll expand our skills with practical examples to help you unlock the full potential of SageMath.

๐Ÿ› ️ Beyond Basics: Advanced Features in the Toolbar

Highlight the additional functionalities of SageMath's interface:

Let's Practice more Examples:

1.    Write python codes to input radius of a sphere and print its surface area and volume.

# Input radius from user

r = float(input("Enter the radius of the sphere: "))


# Surface area of a sphere = 4 * pi * r^2

surface_area = 4 * pi * r^2


# Volume of a sphere = (4/3) * pi * r^3

volume = (4/3) * pi * r^3


Output: 

๐Ÿ’ฌ Understanding the Output

  • Surface Area gives the amount of outer space the sphere occupies.

  • Volume tells us how much space is enclosed inside the sphere.

✅ Try entering values like r = 1, r = 5, or even a decimal like r = 2.5 and observe how the results scale.

๐ŸŽฏ Challenge:

Try modifying the code to calculate the area and volume for multiple spheres. Can you store the values in a list or a dictionary?


2.    Input a positive integer n and integer k<=n. Verify the following properties

# Input values

n = int(input("Enter a positive integer n: "))

k = int(input("Enter an integer k (k <= n): "))


# Check for valid input

if n < 0 or k < 0 or k > n:

    print("Invalid input. Please ensure n >= 0 and 0 <= k <= n.")

else:

    # Define binomial coefficient function

    C = binomial


    # Identity i: nCk = nC(n−k)

    lhs1 = C(n, k)

    rhs1 = C(n, n - k)

    print("\ni. nCk = nC(n-k)")

    print(f"{lhs1} = {rhs1} ->", "Verified ✅" if lhs1 == rhs1 else "Not Verified ❌")


    # Identity ii: k * nCk = n * (n-1)C(k-1)

    lhs2 = k * C(n, k)

    rhs2 = n * C(n - 1, k - 1)

    print("\nii. k × nCk = n × (n−1)C(k−1)")

    print(f"{lhs2} = {rhs2} ->", "Verified ✅" if lhs2 == rhs2 else "Not Verified ❌")


    # Identity iii: nC(k−1) + nCk = (n+1)Ck

    lhs3 = C(n, k - 1) + C(n, k)

    rhs3 = C(n + 1, k)

    print("\niii. nC(k−1) + nCk = (n+1)Ck")

    print(f"{lhs3} = {rhs3} ->", "Verified ✅" if lhs3 == rhs3 else "Not Verified ❌")


Output :

๐Ÿ’ฌ Understanding the Output

These are combinatorial identities often used in probability and algebra:

  • The first identity shows symmetry in combinations.

  • The second connects combinations and multiplication.

  • The third is Pascal's Rule, foundational for Pascal’s Triangle.

๐Ÿ“ธ Visual : Pascal’s Triangle highlighting how nC(k-1) + nCk = (n+1)Ck.


๐ŸŽฏ Challenge:

Can you build Pascal’s Triangle up to n = 10 using a loop? Try printing it in a triangular form!

3.    Input a complex number z and explore some of the properties of z.


SageMath code that takes a complex number

z=a+biz = a + bi  as input and explores the following common properties:

๐Ÿ” Explored Properties:

  1. Real part

  2. Imaginary part

  3. Conjugate

  4. Modulus (absolute value)

  5. Argument (angle in radians)

  6. Polar form

  7.   

# Input complex number as string

z_input = input("Enter a complex number (e.g. 3+4i): ")


# Replace 'i' with 'I' to make it SageMath-friendly

z_input = z_input.replace('i', 'I')


# Evaluate the input string as a SageMath expression

z = sage_eval(z_input)


# Display the entered complex number

print(f"\nComplex number z = {z}")


# Real and Imaginary parts

print("Real part of z:", z.real())

print("Imaginary part of z:", z.imag())


# Conjugate

print("Conjugate of z:", z.conjugate())


# Modulus

print("Modulus (|z|):", abs(z))


# Argument (angle in radians)

print("Argument (arg(z)):", arg(z))


# Polar form

r = abs(z)

theta = arg(z)

print(f"Polar form: {r} * (cos({theta}) + i*sin({theta}))")


# Other computations

print("z squared (z^2):", z^2)

print("Reciprocal (1/z):", 1/z)

print("z * conjugate(z):", z * z.conjugate())


Output: 

Enter a complex number (e.g. 3+4i): 6+i

Complex number z = I + 6
Real part of z: 6
Imaginary part of z: 1
Conjugate of z: -I + 6
Modulus (|z|): sqrt(37)
Argument (arg(z)): arctan(1/6)
Polar form: sqrt(37) * (cos(arctan(1/6)) + i*sin(arctan(1/6)))
z squared (z^2): 12*I + 35
Reciprocal (1/z): -1/37*I + 6/37
z * conjugate(z): 37

๐Ÿ’ฌ Understanding the Output

  • Real & Imaginary Parts break down the number.

  • Conjugate reflects the number across the real axis.

  • Modulus gives the distance from origin (like length of a vector).

  • Argument is the angle from the real axis (in radians).

  • Polar form is useful in trigonometry and electrical engineering.

  • 1/z shows the multiplicative inverse.

  • z * conjugate(z) = square of the modulus.

๐Ÿ“ธ Visual :

A diagram of the complex plane with:

  • Point z plotted

  • Vector from origin

  • Angle (argument)

  • Conjugate as reflected point

๐ŸŽฏ Challenge:

Try plotting the modulus of z = a + bi for various values of a and b (e.g., -5 to 5) and create a 3D surface or contour plot. Share your plots in the comments!

๐Ÿ“Œ Wrapping Up

With these advanced examples and features, you’re no longer just navigating SageMath—you’re mastering it. Next up, we’ll Built-in Data Structures in Python in SageMath.

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