DefParam is the name of an optional arguemt. Its value is a symbol, which specifies the name of the deformation parameter. Its default value is determined by the loadtime configuration Option DefaultDefParam, which has default value t.
For example, we may use the deformation parameter s:
i1 : S=QQ[x_0..x_4]; |
i2 : I=minors(2,matrix {{x_0,x_1,x_2,x_3},{x_1,x_2,x_3,x_4}}); o2 : Ideal of S |
i3 : F0=gens I o3 = | -x_1^2+x_0x_2 -x_1x_2+x_0x_3 -x_2^2+x_1x_3 -x_1x_3+x_0x_4 ------------------------------------------------------------------------ -x_2x_3+x_1x_4 -x_3^2+x_2x_4 | 1 6 o3 : Matrix S <--- S |
i4 : (F,R,G,C)=versalDeformation(F0,DefParam=>s); |
i5 : sum F o5 = | s_1x_1+s_2x_0-x_1^2+x_0x_2 s_4x_0-x_1x_2+x_0x_3 ------------------------------------------------------------------------ -s_1s_4-s_1x_3-s_2x_2+s_4x_1-x_2^2+x_1x_3 ------------------------------------------------------------------------ s_2s_3-s_3^2+s_3x_2-x_1x_3+x_0x_4 ------------------------------------------------------------------------ s_3s_4-s_1x_4-s_2x_3+s_3x_3-x_2x_3+x_1x_4 s_3x_4-s_4x_3-x_3^2+x_2x_4 | 1 6 o5 : Matrix (S[s , s , s , s ]) <--- (S[s , s , s , s ]) 1 2 3 4 1 2 3 4 |