calc_sigma (ul_physlib)

	sigma.r4.v = calc_sigma(z.r4.v, beta_latt.r4.v, disp_latt.r4.v, 
				mom_spread.r4.v, rel_gamma.r4.v, rel_beta.r4.v, 
				norm_emit.r4.v, disp_slope.r4.v,
				alpha_latt.r4.v)

	This routine calculates the transverse rms beam size for a given 
	longitudinal z.

	sigma		returned 
	z		longitudinal z in meters
	beta_latt	beta in meters at z = 0
	alpha_latt	alpha at z = 0
	disp_latt	dispersion in meters at z = 0
	disp_slope	slope of dispersion 
	mom_spread	longitudinal rms momentum spread of bunch (sigmap/p)
	rel_gamma	relativistic gamma
	rel_beta	relativistic beta
	norm_emit	normalized emittance ( x PI) in mm-mrads

	This function returns values as follows:

	-1.0			error occurred
	otherwise		transverse rms beam size in meters

	This function requires the following include files:

	ul_physlib_h:calc_lum_h

	Related functions:

	emitt_dp, calc_lum, qromb_p