try:
        bilin[ii] = (1. / (2. + B)) * ( (2. - B)*bilin[ii - 1] + step[ii] + step[ii - 1] )
        err_text3 = ''
    except ZeroDivisionError, e:
        bilin[ii] = 0
        err_text3 = 'Division by Zero Error'
    except OverflowError:
        bilin[ii] = 0
        err_text3 = 'Stuff with Infinity'