SymPy - Symbolic Mathematics in Python
Overview
SymPy is a Python library for symbolic mathematics that enables exact computation using mathematical symbols rather than numerical approximations. This skill provides comprehensive guidance for performing symbolic algebra, calculus, linear algebra, equation solving, physics calculations, and code generation using SymPy.
When to Use This Skill
Use this skill when:
- Solving equations symbolically (algebraic, differential, systems of equations)
- Performing calculus operations (derivatives, integrals, limits, series)
- Manipulating and simplifying algebraic expressions
- Working with matrices and linear algebra symbolically
- Doing physics calculations (mechanics, quantum mechanics, vector analysis)
- Number theory computations (primes, factorization, modular arithmetic)
- Geometric calculations (2D/3D geometry, analytic geometry)
- Converting mathematical expressions to executable code (Python, C, Fortran)
- Generating LaTeX or other formatted mathematical output
- Needing exact mathematical results (e.g.,
sqrt(2)not1.414...)
Core Capabilities
1. Symbolic Computation Basics
Creating symbols and expressions:
pythonfrom sympy import symbols, Symbol x, y, z = symbols('x y z') expr = x**2 + 2*x + 1 # With assumptions x = symbols('x', real=True, positive=True) n = symbols('n', integer=True)
Simplification and manipulation:
pythonfrom sympy import simplify, expand, factor, cancel simplify(sin(x)**2 + cos(x)**2) # Returns 1 expand((x + 1)**3) # x**3 + 3*x**2 + 3*x + 1 factor(x**2 - 1) # (x - 1)*(x + 1)
For detailed basics: See references/core-capabilities.md
2. Calculus
Derivatives:
pythonfrom sympy import diff diff(x**2, x) # 2*x diff(x**4, x, 3) # 24*x (third derivative) diff(x**2*y**3, x, y) # 6*x*y**2 (partial derivatives)
Integrals:
pythonfrom sympy import integrate, oo integrate(x**2, x) # x**3/3 (indefinite) integrate(x**2, (x, 0, 1)) # 1/3 (definite) integrate(exp(-x), (x, 0, oo)) # 1 (improper)
Limits and Series:
pythonfrom sympy import limit, series limit(sin(x)/x, x, 0) # 1 series(exp(x), x, 0, 6) # 1 + x + x**2/2 + x**3/6 + x**4/24 + x**5/120 + O(x**6)
For detailed calculus operations: See references/core-capabilities.md
3. Equation Solving
Algebraic equations:
pythonfrom sympy import solveset, solve, Eq solveset(x**2 - 4, x) # {-2, 2} solve(Eq(x**2, 4), x) # [-2, 2]
Systems of equations:
pythonfrom sympy import linsolve, nonlinsolve linsolve([x + y - 2, x - y], x, y) # {(1, 1)} (linear) nonlinsolve([x**2 + y - 2, x + y**2 - 3], x, y) # (nonlinear)
Differential equations:
pythonfrom sympy import Function, dsolve, Derivative f = symbols('f', cls=Function) dsolve(Derivative(f(x), x) - f(x), f(x)) # Eq(f(x), C1*exp(x))
For detailed solving methods: See references/core-capabilities.md
4. Matrices and Linear Algebra
Matrix creation and operations:
pythonfrom sympy import Matrix, eye, zeros M = Matrix([[1, 2], [3, 4]]) M_inv = M**-1 # Inverse M.det() # Determinant M.T # Transpose
Eigenvalues and eigenvectors:
pythoneigenvals = M.eigenvals() # {eigenvalue: multiplicity} eigenvects = M.eigenvects() # [(eigenval, mult, [eigenvectors])] P, D = M.diagonalize() # M = P*D*P^-1
Solving linear systems:
pythonA = Matrix([[1, 2], [3, 4]]) b = Matrix([5, 6]) x = A.solve(b) # Solve Ax = b
For comprehensive linear algebra: See references/matrices-linear-algebra.md
5. Physics and Mechanics
Classical mechanics:
pythonfrom sympy.physics.mechanics import dynamicsymbols, LagrangesMethod from sympy import symbols # Define system q = dynamicsymbols('q') m, g, l = symbols('m g l') # Lagrangian (T - V) L = m*(l*q.diff())**2/2 - m*g*l*(1 - cos(q)) # Apply Lagrange's method LM = LagrangesMethod(L, [q])
Vector analysis:
pythonfrom sympy.physics.vector import ReferenceFrame, dot, cross N = ReferenceFrame('N') v1 = 3*N.x + 4*N.y v2 = 1*N.x + 2*N.z dot(v1, v2) # Dot product cross(v1, v2) # Cross product
Quantum mechanics:
pythonfrom sympy.physics.quantum import Ket, Bra, Commutator psi = Ket('psi') A = Operator('A') comm = Commutator(A, B).doit()
For detailed physics capabilities: See references/physics-mechanics.md
6. Advanced Mathematics
The skill includes comprehensive support for:
- Geometry: 2D/3D analytic geometry, points, lines, circles, polygons, transformations
- Number Theory: Primes, factorization, GCD/LCM, modular arithmetic, Diophantine equations
- Combinatorics: Permutations, combinations, partitions, group theory
- Logic and Sets: Boolean logic, set theory, finite and infinite sets
- Statistics: Probability distributions, random variables, expectation, variance
- Special Functions: Gamma, Bessel, orthogonal polynomials, hypergeometric functions
- Polynomials: Polynomial algebra, roots, factorization, Groebner bases
For detailed advanced topics: See references/advanced-topics.md
7. Code Generation and Output
Convert to executable functions:
pythonfrom sympy import lambdify import numpy as np expr = x**2 + 2*x + 1 f = lambdify(x, expr, 'numpy') # Create NumPy function x_vals = np.linspace(0, 10, 100) y_vals = f(x_vals) # Fast numerical evaluation
Generate C/Fortran code:
pythonfrom sympy.utilities.codegen import codegen [(c_name, c_code), (h_name, h_header)] = codegen( ('my_func', expr), 'C' )
LaTeX output:
pythonfrom sympy import latex latex_str = latex(expr) # Convert to LaTeX for documents
For comprehensive code generation: See references/code-generation-printing.md
Working with SymPy: Best Practices
1. Always Define Symbols First
pythonfrom sympy import symbols x, y, z = symbols('x y z') # Now x, y, z can be used in expressions
2. Use Assumptions for Better Simplification
pythonx = symbols('x', positive=True, real=True) sqrt(x**2) # Returns x (not Abs(x)) due to positive assumption
Common assumptions: real, positive, negative, integer, rational, complex, even, odd
3. Use Exact Arithmetic
pythonfrom sympy import Rational, S # Correct (exact): expr = Rational(1, 2) * x expr = S(1)/2 * x # Incorrect (floating-point): expr = 0.5 * x # Creates approximate value
4. Numerical Evaluation When Needed
pythonfrom sympy import pi, sqrt result = sqrt(8) + pi result.evalf() # 5.96371554103586 result.evalf(50) # 50 digits of precision
5. Convert to NumPy for Performance
python# Slow for many evaluations: for x_val in range(1000): result = expr.subs(x, x_val).evalf() # Fast: f = lambdify(x, expr, 'numpy') results = f(np.arange(1000))
6. Use Appropriate Solvers
solveset: Algebraic equations (primary)linsolve: Linear systemsnonlinsolve: Nonlinear systemsdsolve: Differential equationssolve: General purpose (legacy, but flexible)
Reference Files Structure
This skill uses modular reference files for different capabilities:
-
core-capabilities.md: Symbols, algebra, calculus, simplification, equation solving- Load when: Basic symbolic computation, calculus, or solving equations
-
matrices-linear-algebra.md: Matrix operations, eigenvalues, linear systems- Load when: Working with matrices or linear algebra problems
-
physics-mechanics.md: Classical mechanics, quantum mechanics, vectors, units- Load when: Physics calculations or mechanics problems
-
advanced-topics.md: Geometry, number theory, combinatorics, logic, statistics- Load when: Advanced mathematical topics beyond basic algebra and calculus
-
code-generation-printing.md: Lambdify, codegen, LaTeX output, printing- Load when: Converting expressions to code or generating formatted output
Common Use Case Patterns
Pattern 1: Solve and Verify
pythonfrom sympy import symbols, solve, simplify x = symbols('x') # Solve equation equation = x**2 - 5*x + 6 solutions = solve(equation, x) # [2, 3] # Verify solutions for sol in solutions: result = simplify(equation.subs(x, sol)) assert result == 0
Pattern 2: Symbolic to Numeric Pipeline
python# 1. Define symbolic problem x, y = symbols('x y') expr = sin(x) + cos(y) # 2. Manipulate symbolically simplified = simplify(expr) derivative = diff(simplified, x) # 3. Convert to numerical function f = lambdify((x, y), derivative, 'numpy') # 4. Evaluate numerically results = f(x_data, y_data)
Pattern 3: Document Mathematical Results
python# Compute result symbolically integral_expr = Integral(x**2, (x, 0, 1)) result = integral_expr.doit() # Generate documentation print(f"LaTeX: {latex(integral_expr)} = {latex(result)}") print(f"Pretty: {pretty(integral_expr)} = {pretty(result)}") print(f"Numerical: {result.evalf()}")
Integration with Scientific Workflows
With NumPy
pythonimport numpy as np from sympy import symbols, lambdify x = symbols('x') expr = x**2 + 2*x + 1 f = lambdify(x, expr, 'numpy') x_array = np.linspace(-5, 5, 100) y_array = f(x_array)
With Matplotlib
pythonimport matplotlib.pyplot as plt import numpy as np from sympy import symbols, lambdify, sin x = symbols('x') expr = sin(x) / x f = lambdify(x, expr, 'numpy') x_vals = np.linspace(-10, 10, 1000) y_vals = f(x_vals) plt.plot(x_vals, y_vals) plt.show()
With SciPy
pythonfrom scipy.optimize import fsolve from sympy import symbols, lambdify # Define equation symbolically x = symbols('x') equation = x**3 - 2*x - 5 # Convert to numerical function f = lambdify(x, equation, 'numpy') # Solve numerically with initial guess solution = fsolve(f, 2)
Quick Reference: Most Common Functions
python# Symbols from sympy import symbols, Symbol x, y = symbols('x y') # Basic operations from sympy import simplify, expand, factor, collect, cancel from sympy import sqrt, exp, log, sin, cos, tan, pi, E, I, oo # Calculus from sympy import diff, integrate, limit, series, Derivative, Integral # Solving from sympy import solve, solveset, linsolve, nonlinsolve, dsolve # Matrices from sympy import Matrix, eye, zeros, ones, diag # Logic and sets from sympy import And, Or, Not, Implies, FiniteSet, Interval, Union # Output from sympy import latex, pprint, lambdify, init_printing # Utilities from sympy import evalf, N, nsimplify
Getting Started Examples
Example 1: Solve Quadratic Equation
pythonfrom sympy import symbols, solve, sqrt x = symbols('x') solution = solve(x**2 - 5*x + 6, x) # [2, 3]
Example 2: Calculate Derivative
pythonfrom sympy import symbols, diff, sin x = symbols('x') f = sin(x**2) df_dx = diff(f, x) # 2*x*cos(x**2)
Example 3: Evaluate Integral
pythonfrom sympy import symbols, integrate, exp x = symbols('x') integral = integrate(x * exp(-x**2), (x, 0, oo)) # 1/2
Example 4: Matrix Eigenvalues
pythonfrom sympy import Matrix M = Matrix([[1, 2], [2, 1]]) eigenvals = M.eigenvals() # {3: 1, -1: 1}
Example 5: Generate Python Function
pythonfrom sympy import symbols, lambdify import numpy as np x = symbols('x') expr = x**2 + 2*x + 1 f = lambdify(x, expr, 'numpy') f(np.array([1, 2, 3])) # array([ 4, 9, 16])
Troubleshooting Common Issues
-
"NameError: name 'x' is not defined"
- Solution: Always define symbols using
symbols()before use
- Solution: Always define symbols using
-
Unexpected numerical results
- Issue: Using floating-point numbers like
0.5instead ofRational(1, 2) - Solution: Use
Rational()orS()for exact arithmetic
- Issue: Using floating-point numbers like
-
Slow performance in loops
- Issue: Using
subs()andevalf()repeatedly - Solution: Use
lambdify()to create a fast numerical function
- Issue: Using
-
"Can't solve this equation"
- Try different solvers:
solve,solveset,nsolve(numerical) - Check if the equation is solvable algebraically
- Use numerical methods if no closed-form solution exists
- Try different solvers:
-
Simplification not working as expected
- Try different simplification functions:
simplify,factor,expand,trigsimp - Add assumptions to symbols (e.g.,
positive=True) - Use
simplify(expr, force=True)for aggressive simplification
- Try different simplification functions:
Additional Resources
- Official Documentation: https://docs.sympy.org/
- Tutorial: https://docs.sympy.org/latest/tutorials/intro-tutorial/index.html
- API Reference: https://docs.sympy.org/latest/reference/index.html
- Examples: https://github.com/sympy/sympy/tree/master/examples

