For ice I melting pressure as a function of temperature:
$$\pi = 1- 0.626000 \times 10^6 (1- \theta^{-3}) + 0.197135 \times 10^6 (1- \theta^{21.2})$$
where
$\pi =$ (pressure in MPa)/0.000611657 MPa
$\theta =$ (temperature in kelvins)/273.16K
Source is International Equation of the Pressure along the Melting and along the Sublimation Curve of Ordinary Water substance (no paywall).
For carbon dioxide:
$$\frac{p_m}{p_n} = 1 + a_1 (\frac{T}{T_t}) + a_2 (\frac{T}{T_t})^2$$
Where:
$T$ is temperature in kelvins
$T_t =$ 216.592K
$p_m$ is the melting pressure in MPa
$p_n =$ 0.51795 MPa
$a_1 =$ 1955.5390
$a_2 =$ 2055.4593
Source is A New Equation of State for Carbon Dioxide... (no paywall)
Check original sources before using equations in case I made typo(s).