Changeset 5575:c186846c332a

Timestamp:

08/01/07 19:50:02 (6 years ago)

Author:

William Stein <wstein@…>

Branch:

default

Message:

code from Didier.

File:

• sage/rings/polynomial/multi_polynomial_ring_generic.pyx (modified) (2 diffs)

sage/rings/polynomial/multi_polynomial_ring_generic.pyx

@@ -5 +5 @@
 import multi_polynomial_ideal
 from term_order import TermOrder
+from sage.rings.integer_ring import ZZ
+from sage.rings.polynomial.polydict import PolyDict
+import multi_polynomial_element
 
 def is_MPolynomialRing(x):
@@ -250 +253 @@
 
 
+    def random_element(self,degree,terms=5,*args,**kwds):
+        """
+        Generate a random polynomial in this ring
+        INPUT:
+            degree -- maximum total degree of resulting polynomial
+            terms  -- maximum number of terms to generate
+
+        OUTPOUT: a random polynomial of total degree \code{degree}
+                and with \code{term} terms in it
+
+        EXAMPLES:
+        sage: R = MPolynomialRing(ZZ, 'x,y',2 );
+        sage: R.random_element(2) #random
+        -1*x*y + x + 15*y - 2
+ 
+        sage: R.random_element(12) #random
+        x^4*y^5 + x^3*y^5 + 6*x^2*y^2 - x^2
+
+        sage: R.random_element(12,3) #random
+        -3*x^4*y^2 - x^5 - x^4*y
+
+        sage: R.random_element(3) # random
+        2*y*z + 2*x + 2*y
+
+        sage:  R = MPolynomialRing(RR, 'x,y',2 );
+        sage: R.random_element(2) # random
+        -0.645358174399450*x*y + 0.572655401740132*x + 0.197478565033010
+
+        sage: R.random_element(41) # random
+        -4*x^6*y^4*z^4*a^6*b^3*c^6*d^5 + 1/2*x^4*y^3*z^5*a^4*c^5*d^6 - 5*x^3*z^3*a^6*b^4*c*d^5 + 10*x^2*y*z^5*a^4*b^2*c^3*d^4 - 5*x^3*y^5*z*b^2*c^5*d
+
+        AUTHOR:
+            -- didier deshommes
+        """
+        # General strategy:
+        # generate n-tuples of numbers with each element in the tuple
+        # not greater than  (degree/n) so that the degree 
+        # (ie, the sum of the elements in the tuple) does not exceed
+        # their total degree
+        
+        n = self.__ngens         # length of the n-tuple
+        max_deg = int(degree/n)  # max degree for each term
+        R = self.base_ring()
+        
+        # restrict exponents to positive integers only
+        _exponents = [ tuple([ZZ.random_element(0,max_deg+1) for _ in range(n)])
+                       for _ in range(terms) ]
+        _coeffs = [R.random_element(*args,**kwds) for _ in range(terms)]
+
+        d = dict( zip(tuple(_exponents),_coeffs) ) 
+        return self(multi_polynomial_element.MPolynomial_polydict(self, PolyDict(d)))
+        
+        
 ####################
 # Leave *all* old versions!