Added usage of more correct exceptions.

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/functions/AbstractPolynomial.kt

@@ -295,7 +295,7 @@ public interface AbstractPolynomialSpace<C, P: AbstractPolynomial<C>> : Ring<P>
      * If polynomial is a constant polynomial represents and returns it as constant.
      * Otherwise, (when the polynomial is not constant polynomial) raises corresponding exception.
      */
-    public fun P.asConstant(): C = asConstantOrNull() ?: error("Can not represent non-constant polynomial as a constant")
+    public fun P.asConstant(): C = requireNotNull(asConstantOrNull()) { "Can not represent non-constant polynomial as a constant" }
 
     override fun add(left: P, right: P): P = left + right
     override fun multiply(left: P, right: P): P = left * right

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/functions/AbstractRationalFunction.kt

@@ -460,7 +460,7 @@ public interface AbstractRationalFunctionalSpace<C, P: AbstractPolynomial<C>, R:
      * If polynomial is a constant polynomial represents and returns it as constant.
      * Otherwise, (when the polynomial is not constant polynomial) raises corresponding exception.
      */
-    public fun P.asConstant(): C = asConstantOrNull() ?: error("Can not represent non-constant polynomial as a constant")
+    public fun P.asConstant(): C = requireNotNull(asConstantOrNull()) { "Can not represent non-constant polynomial as a constant" }
 
     /**
      * Degree of the polynomial, [see also](https://en.wikipedia.org/wiki/Degree_of_a_polynomial). If the polynomial is

kmath-functions/src/commonTest/kotlin/space/kscience/kmath/functions/PolynomialUtilTest.kt

@@ -11,6 +11,7 @@ import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
 
+
 class PolynomialUtilTest {
     @Test
     fun test_substitute_Double() {