Check isdiag in dense trig functions (JuliaLang#56483)

This improves performance for dense diagonal matrices, as we may apply
the function only to the diagonal elements.
```julia
julia> A = diagm(0=>rand(100));

julia> @Btime cos($A);
  349.211 μs (22 allocations: 401.58 KiB) # nightly v"1.12.0-DEV.1571"
  16.215 μs (7 allocations: 80.02 KiB) # this PR
```

---------

Co-authored-by: Daniel Karrasch <[email protected]>

Author: jishnub

stdlib/LinearAlgebra/src/dense.jl

@@ -683,7 +683,12 @@ Base.:^(::Irrational{:ℯ}, A::AbstractMatrix) = exp(A)
 ## "Functions of Matrices: Theory and Computation", SIAM
 function exp!(A::StridedMatrix{T}) where T<:BlasFloat
     n = checksquare(A)
-    if ishermitian(A)
+    if isdiag(A)
+        for i in diagind(A, IndexStyle(A))
+            A[i] = exp(A[i])
+        end
+        return A
+    elseif ishermitian(A)
         return copytri!(parent(exp(Hermitian(A))), 'U', true)
     end
     ilo, ihi, scale = LAPACK.gebal!('B', A)    # modifies A
@@ -1014,9 +1019,16 @@ end
 cbrt(A::AdjointAbsMat) = adjoint(cbrt(parent(A)))
 cbrt(A::TransposeAbsMat) = transpose(cbrt(parent(A)))
 
+function applydiagonal(f, A)
+    dinv = f(Diagonal(A))
+    copyto!(similar(A, eltype(dinv)), dinv)
+end
+
 function inv(A::StridedMatrix{T}) where T
     checksquare(A)
-    if istriu(A)
+    if isdiag(A)
+        Ai = applydiagonal(inv, A)
+    elseif istriu(A)
         Ai = triu!(parent(inv(UpperTriangular(A))))
     elseif istril(A)
         Ai = tril!(parent(inv(LowerTriangular(A))))
@@ -1044,14 +1056,18 @@ julia> cos(fill(1.0, (2,2)))
 ```
 """
 function cos(A::AbstractMatrix{<:Real})
-    if issymmetric(A)
+    if isdiag(A)
+        return applydiagonal(cos, A)
+    elseif issymmetric(A)
         return copytri!(parent(cos(Symmetric(A))), 'U')
     end
     T = complex(float(eltype(A)))
     return real(exp!(T.(im .* A)))
 end
 function cos(A::AbstractMatrix{<:Complex})
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(cos, A)
+    elseif ishermitian(A)
         return copytri!(parent(cos(Hermitian(A))), 'U', true)
     end
     T = complex(float(eltype(A)))
@@ -1077,14 +1093,18 @@ julia> sin(fill(1.0, (2,2)))
 ```
 """
 function sin(A::AbstractMatrix{<:Real})
-    if issymmetric(A)
+    if isdiag(A)
+        return applydiagonal(sin, A)
+    elseif issymmetric(A)
         return copytri!(parent(sin(Symmetric(A))), 'U')
     end
     T = complex(float(eltype(A)))
     return imag(exp!(T.(im .* A)))
 end
 function sin(A::AbstractMatrix{<:Complex})
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(sin, A)
+    elseif ishermitian(A)
         return copytri!(parent(sin(Hermitian(A))), 'U', true)
     end
     T = complex(float(eltype(A)))
@@ -1163,7 +1183,9 @@ julia> tan(fill(1.0, (2,2)))
 ```
 """
 function tan(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(tan, A)
+    elseif ishermitian(A)
         return copytri!(parent(tan(Hermitian(A))), 'U', true)
     end
     S, C = sincos(A)
@@ -1177,7 +1199,9 @@ end
 Compute the matrix hyperbolic cosine of a square matrix `A`.
 """
 function cosh(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(cosh, A)
+    elseif ishermitian(A)
         return copytri!(parent(cosh(Hermitian(A))), 'U', true)
     end
     X = exp(A)
@@ -1191,7 +1215,9 @@ end
 Compute the matrix hyperbolic sine of a square matrix `A`.
 """
 function sinh(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(sinh, A)
+    elseif ishermitian(A)
         return copytri!(parent(sinh(Hermitian(A))), 'U', true)
     end
     X = exp(A)
@@ -1205,7 +1231,9 @@ end
 Compute the matrix hyperbolic tangent of a square matrix `A`.
 """
 function tanh(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(tanh, A)
+    elseif ishermitian(A)
         return copytri!(parent(tanh(Hermitian(A))), 'U', true)
     end
     X = exp(A)
@@ -1240,7 +1268,9 @@ julia> acos(cos([0.5 0.1; -0.2 0.3]))
 ```
 """
 function acos(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(acos, A)
+    elseif ishermitian(A)
         acosHermA = acos(Hermitian(A))
         return isa(acosHermA, Hermitian) ? copytri!(parent(acosHermA), 'U', true) : parent(acosHermA)
     end
@@ -1271,7 +1301,9 @@ julia> asin(sin([0.5 0.1; -0.2 0.3]))
 ```
 """
 function asin(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(asin, A)
+    elseif ishermitian(A)
         asinHermA = asin(Hermitian(A))
         return isa(asinHermA, Hermitian) ? copytri!(parent(asinHermA), 'U', true) : parent(asinHermA)
     end
@@ -1302,7 +1334,9 @@ julia> atan(tan([0.5 0.1; -0.2 0.3]))
 ```
 """
 function atan(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(atan, A)
+    elseif ishermitian(A)
         return copytri!(parent(atan(Hermitian(A))), 'U', true)
     end
     SchurF = Schur{Complex}(schur(A))
@@ -1320,7 +1354,9 @@ logarithmic formulas used to compute this function, see [^AH16_4].
 [^AH16_4]: Mary Aprahamian and Nicholas J. Higham, "Matrix Inverse Trigonometric and Inverse Hyperbolic Functions: Theory and Algorithms", MIMS EPrint: 2016.4. [https://doi.org/10.1137/16M1057577](https://doi.org/10.1137/16M1057577)
 """
 function acosh(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(acosh, A)
+    elseif ishermitian(A)
         acoshHermA = acosh(Hermitian(A))
         return isa(acoshHermA, Hermitian) ? copytri!(parent(acoshHermA), 'U', true) : parent(acoshHermA)
     end
@@ -1339,7 +1375,9 @@ logarithmic formulas used to compute this function, see [^AH16_5].
 [^AH16_5]: Mary Aprahamian and Nicholas J. Higham, "Matrix Inverse Trigonometric and Inverse Hyperbolic Functions: Theory and Algorithms", MIMS EPrint: 2016.4. [https://doi.org/10.1137/16M1057577](https://doi.org/10.1137/16M1057577)
 """
 function asinh(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(asinh, A)
+    elseif ishermitian(A)
         return copytri!(parent(asinh(Hermitian(A))), 'U', true)
     end
     SchurF = Schur{Complex}(schur(A))
@@ -1357,7 +1395,9 @@ logarithmic formulas used to compute this function, see [^AH16_6].
 [^AH16_6]: Mary Aprahamian and Nicholas J. Higham, "Matrix Inverse Trigonometric and Inverse Hyperbolic Functions: Theory and Algorithms", MIMS EPrint: 2016.4. [https://doi.org/10.1137/16M1057577](https://doi.org/10.1137/16M1057577)
 """
 function atanh(A::AbstractMatrix)
-    if ishermitian(A)
+    if isdiag(A)
+        return applydiagonal(atanh, A)
+    elseif ishermitian(A)
         return copytri!(parent(atanh(Hermitian(A))), 'U', true)
     end
     SchurF = Schur{Complex}(schur(A))

stdlib/LinearAlgebra/test/dense.jl

@@ -607,15 +607,16 @@ end
                        -0.4579038628067864 1.7361475641080275 6.478801851038108])
         A3 = convert(Matrix{elty}, [0.25 0.25; 0 0])
         A4 = convert(Matrix{elty}, [0 0.02; 0 0])
+        A5 = convert(Matrix{elty}, [2.0 0; 0 3.0])
 
         cosA1 = convert(Matrix{elty},[-0.18287716254368605 -0.29517205254584633 0.761711400552759;
                                       0.23326967400345625 0.19797853773269333 -0.14758602627292305;
                                       0.23326967400345636 0.6141253742798355 -0.5637328628200653])
         sinA1 = convert(Matrix{elty}, [0.2865568596627417 -1.107751980582015 -0.13772915374386513;
                                        -0.6227405671629401 0.2176922827908092 -0.5538759902910078;
                                        -0.6227405671629398 -0.6916051440348725 0.3554214365346742])
-        @test cos(A1) ≈ cosA1
-        @test sin(A1) ≈ sinA1
+        @test @inferred(cos(A1)) ≈ cosA1
+        @test @inferred(sin(A1)) ≈ sinA1
 
         cosA2 = convert(Matrix{elty}, [-0.6331745163802187 0.12878366262380136 -0.17304181968301532;
                                        0.12878366262380136 -0.5596234510748788 0.5210483146041339;
@@ -637,36 +638,36 @@ end
         @test sin(A4) ≈ sinA4
 
         # Identities
-        for (i, A) in enumerate((A1, A2, A3, A4))
-            @test sincos(A) == (sin(A), cos(A))
+        for (i, A) in enumerate((A1, A2, A3, A4, A5))
+            @test @inferred(sincos(A)) == (sin(A), cos(A))
             @test cos(A)^2 + sin(A)^2 ≈ Matrix(I, size(A))
             @test cos(A) ≈ cos(-A)
             @test sin(A) ≈ -sin(-A)
-            @test tan(A) ≈ sin(A) / cos(A)
+            @test @inferred(tan(A)) ≈ sin(A) / cos(A)
 
             @test cos(A) ≈ real(exp(im*A))
             @test sin(A) ≈ imag(exp(im*A))
             @test cos(A) ≈ real(cis(A))
             @test sin(A) ≈ imag(cis(A))
-            @test cis(A) ≈ cos(A) + im * sin(A)
+            @test @inferred(cis(A)) ≈ cos(A) + im * sin(A)
 
-            @test cosh(A) ≈ 0.5 * (exp(A) + exp(-A))
-            @test sinh(A) ≈ 0.5 * (exp(A) - exp(-A))
-            @test cosh(A) ≈ cosh(-A)
-            @test sinh(A) ≈ -sinh(-A)
+            @test @inferred(cosh(A)) ≈ 0.5 * (exp(A) + exp(-A))
+            @test @inferred(sinh(A)) ≈ 0.5 * (exp(A) - exp(-A))
+            @test @inferred(cosh(A)) ≈ cosh(-A)
+            @test @inferred(sinh(A)) ≈ -sinh(-A)
 
             # Some of the following identities fail for A3, A4 because the matrices are singular
-            if i in (1, 2)
-                @test sec(A) ≈ inv(cos(A))
-                @test csc(A) ≈ inv(sin(A))
-                @test cot(A) ≈ inv(tan(A))
-                @test sech(A) ≈ inv(cosh(A))
-                @test csch(A) ≈ inv(sinh(A))
-                @test coth(A) ≈ inv(tanh(A))
+            if i in (1, 2, 5)
+                @test @inferred(sec(A)) ≈ inv(cos(A))
+                @test @inferred(csc(A)) ≈ inv(sin(A))
+                @test @inferred(cot(A)) ≈ inv(tan(A))
+                @test @inferred(sech(A)) ≈ inv(cosh(A))
+                @test @inferred(csch(A)) ≈ inv(sinh(A))
+                @test @inferred(coth(A)) ≈ inv(@inferred tanh(A))
             end
             # The following identities fail for A1, A2 due to rounding errors;
             # probably needs better algorithm for the general case
-            if i in (3, 4)
+            if i in (3, 4, 5)
                 @test cosh(A)^2 - sinh(A)^2 ≈ Matrix(I, size(A))
                 @test tanh(A) ≈ sinh(A) / cosh(A)
             end