Add error handling for vector expressions

Fixes #58 and #106 by throwing an informative error when vector expressions are passed to integrate().

The error message guides users to use element-wise integration instead: integrate.([expr1, expr2, ...], x)

Added tests to verify:
- Vector expressions throw appropriate error
- Scalar integration still works
- Element-wise integration works as expected

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

simple_test.jl

@@ -0,0 +1,31 @@
+using Pkg
+Pkg.activate(".")
+
+# Force load the package
+using SymbolicNumericIntegration
+using Symbolics
+
+println("Testing vector expression error handling...")
+
+# Test case 1: Vector with symbolic variables
+@variables x
+try
+    result = integrate([x])
+    println("❌ Test 1 FAILED: Should have thrown an error but got: $result")
+catch e
+    if occursin("Vector expressions are not supported", string(e))
+        println("✅ Test 1 PASSED: Vector input correctly rejected")
+    else
+        println("❌ Test 1 FAILED: Wrong error message: $(e)")
+    end
+end
+
+# Test case 2: Scalar integration should still work
+try
+    result = integrate(x)
+    println("✅ Test 2 PASSED: Scalar integration works: $result")
+catch e
+    println("❌ Test 2 FAILED: Scalar integration should work but got: $(e)")
+end
+
+println("\nAll tests completed!")

src/integral.jl

@@ -72,6 +72,11 @@ function integrate(eq, x = nothing;
         detailed = true)
     deprecation_warnings(; homotopy, use_optim)
 
+    # Check if eq is a vector/array expression and throw an error
+    if eq isa AbstractArray || eq isa AbstractVector
+        error("Vector expressions are not supported. Please use element-wise integration with `integrate.([expr1, expr2, ...], x)` instead.")
+    end
+
     eq = expand(eq)
 
     if x == nothing

test/runtests.jl

@@ -327,3 +327,21 @@ end
         num_trials = 10)
     @test n > 0
 end
+
+@testset "vector expression error handling" begin
+    @variables x α
+
+    # Test that vector expressions throw an appropriate error
+    @test_throws ErrorException("Vector expressions are not supported. Please use element-wise integration with `integrate.([expr1, expr2, ...], x)` instead.") integrate([x])
+    @test_throws ErrorException("Vector expressions are not supported. Please use element-wise integration with `integrate.([expr1, expr2, ...], x)` instead.") integrate([1, 2 * α], α)
+
+    # Test that scalar integration still works
+    @test integrate(x) == ((1//2)*(x^2), 0, 0)
+    @test integrate(2 * α, α) == (α^2, 0, 0)
+
+    # Test that element-wise integration works
+    results = integrate.([1, 2 * α], α)
+    @test length(results) == 2
+    @test results[1] == (α, 0, 0)
+    @test results[2] == (α^2, 0, 0)
+end

test_vector_fix.jl

@@ -0,0 +1,47 @@
+using Pkg
+Pkg.activate(".")
+using Symbolics, SymbolicNumericIntegration
+
+println("Testing vector expression error handling:")
+println()
+
+# Test case from issue #58
+@variables α
+exp2 = [1, 2 * α]
+
+println("Test 1: integrate([1, 2α], α)")
+try
+    result = integrate(exp2, α)
+    println("ERROR: Should have thrown an error but got: $result")
+catch e
+    println("✓ Correctly caught error: $(e)")
+end
+
+println()
+println("Test 2: Verify element-wise integration still works")
+try
+    result = integrate.(exp2, α)
+    println("✓ Element-wise integration works: $result")
+catch e
+    println("ERROR: Element-wise should work but got: $(e)")
+end
+
+println()
+# Test case from issue #106
+@variables x
+println("Test 3: integrate([x])")
+try
+    result = integrate([x])
+    println("ERROR: Should have thrown an error but got: $result")
+catch e
+    println("✓ Correctly caught error: $(e)")
+end
+
+println()
+println("Test 4: Verify scalar integration still works")
+try
+    result = integrate(2 * α, α)
+    println("✓ Scalar integration works: $result")
+catch e
+    println("ERROR: Scalar should work but got: $(e)")
+end