how calculate the discriminator by the struct to resolve the command in the anchor project?

Question

i got the discriminator by the command : anchor build. but i wonder how can i got this discriminator without the command. i search the source code and it use ${namespace}:${context} and hash-sha256. but i got the different result in my code. this is my command:

pub fn initialize_pool_secure(ctx: Context<InitializePoolSecure>) -> Result<()> {}

can anyone do me a favour?