Taylor expand equations

JuliaSymbolics · Oct 8, 2024 · cb9343d · cb9343d
1 parent 92dfd5f
commit cb9343d
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diff --git a/src/taylor.jl b/src/taylor.jl
@@ -17,6 +17,9 @@ function taylor_coeff(f, x, n; rationalize=true)
     end
     return c
 end
+function taylor_coeff(eq::Equation, args...; kwargs...)
+    return taylor_coeff(eq.lhs, args...; kwargs...) ~ taylor_coeff(eq.rhs, args...; kwargs...)
+end
 
 """
     taylor(f, x, [x0=0,] n; rationalize=true)
@@ -56,3 +59,6 @@ function taylor(f, x, x0, n; kwargs...)
     # 3) substitute back x = x′ + x0
     return substitute(s, x′ => x - x0)
 end
+function taylor(eq::Equation, args...; kwargs...)
+    return taylor(eq.lhs, args...; kwargs...) ~ taylor(eq.rhs, args...; kwargs...)
+end
diff --git a/test/taylor.jl b/test/taylor.jl
@@ -26,3 +26,9 @@ end
 
 # around x ≠ 0
 @test substitute(taylor(√(x), x, 1, 0:6), x => x + 1) - taylor(√(1+x), x, 0:6) == 0
+
+# equations
+eq = sin(2*x) ~ 2*sin(x)*cos(x)
+eq = taylor(eq, x, 0:7)
+eqs = [Symbolics.taylor_coeff(eq, x, n) for n in 0:7]
+@test all(isequal(eq.lhs, eq.rhs) for eq in eqs)