Today's blog post of Fractint compatible gifs and anti-aliased jpgs is of two versions of the field4_jul formula by Kerry Mitchell. They are identical except for the imaginary P2 values. I calculated with values of 0 and 12. Available at http://maxitersfractalfollies.blogspot.com I've posted only one version of the par file, just vary imag(P2) if regenerating. Field Line Variations { ; fract506.gif ; blank ; calctime 0:03:55.63 ; created Nov 08, 2010 ; Fractint Version 2004 Patchlevel 10 reset=2004 type=formula formulafile=*.frm formulaname=field4_jul center-mag=0.048197/0.607759/3.404629 params=0.375/0.375/1000000/0 float=y maxiter=1500 inside=0 decomp=256 periodicity=0 colors=00101211312412413523624724825935936A36B37C47D48E48F49F59G5AH5AI5B\ J6BK6CK6CL6DM7DN7EO7EP7FP8FQ8GR8GS9HT9HU9IUAIVAJWAJXBKXBKYBLYCLZCMZCM_DN\ `DN`DOaDOaEPbEPbEQcFQcFRdFReGReGSfGSfHTgHTgHUhIUiIViIVjIWjJWkJXkJXlKYlKY\ mLZnLZnM_oM_oM`oN`pNapOaqObqPbrPcrPcrQdrQdsResRetRftSftSgtTguThuUhuUivVi\ vVjvVjvWkwXkwYlwYlwZmxZmx_nx_nx`ox`oxapyapybqybqycrydryesyeszftzgtzhuzhu\ zivzjvzkwzmwznxzpxzqyzryzuzzuzzuzzryzqyzoxznxzmwzkwzjvzivziuzhuzgtzftzfs\ zesydrycrybqybqyapyapy`ox_ox_nxZnxZmxYmwYlwXlwXkwWkwVjvVjvVivVivUhvUhuTg\ uTguSfuSftRetQesQdsQdrPcrPcrObqObqOapNapN`oN`oM_nM_nMZmLZmLYlLYlKYlKXkJX\ kJWjJWjIViIViIUhHUhHTgHTgGSfGSfFRfFReFQdFQcEPcEPbEObDOaDNaDN`CM_CM_BLZBL\ ZBKYAKYAJXAJWAIV9IU9HU9HT8GS8GR8FR8FQ7EP7EO7DN7DM6CL6CL6BK6BJ5AI5AH59G59\ G48F48E47D37C36B36A35A259248247236135124124113012001000 } frm:field4_jul { ; Kerry Mitchell 20jan98 ; ; Colors Julia sets by nearest approach to ; period 4 field lines ; ; use decomp=256 ; p1 = Julia parameter ; real(p2) = bailout (try 1e12) ; imag(p2) = number of field line to use: 0 - 15 ; 4 iterations per pixel ; variable zc used for calculation, z for coloring ; zc=pixel, c=p1, maxr=real(p2), minr=maxr, iter=1 fieldangle=tan(imag(p2)*2*pi/15): ; ; iteration ; compare tangent of polar angle with desired ; field line angle, update minimum if needed ; iter=iter+4, zc=sqr(zc)+c, zc=sqr(zc)+c, zc=sqr(zc)+c zc=sqr(zc)+c, rzc=|zc|, tanangle=imag(zc)/real(zc), r=cabs(fieldangle-tanangle) if (r<minr) minr=r end if ; ; bailout ; set "iteration done" flag (iter=-1) ; use log of minimum difference of angles as ; decomposition angle ; if ((rzc>maxr)||(iter>=maxit)) iter=-1 angle=log(minr) z=cos(angle)+flip(sin(angle)) end if iter>0 } Roger Alexander