[Quantlib-users] Query on Calendar spread options

[Ashish B. <ash...@gm...>]

Hi,

I use the Blackscholes engine to evaluate the commodity options. However,
it supports only positive strikes and throws error for a negative strike.

Now, I wish to evaluate the spread options traded on CBOT:
Consecutive Corn CSO Quotes - CME Group
<https://www.cmegroup.com/markets/agriculture/grains/corn.quotes.options.html#optionProductId=2730>

How can I evaluate these using Quantlib? Any suggestions on the correct
engine to use which supports the negative strike?

Thanks
Ashish Bansal