Partial Lot Subsidy API

Version 1.0 • Content-Type: application/json

Compute the subsidy amount required to cover unsold units in a fixed lot and the resulting new unit price to fully amortize the lot when a buyer purchases only a partial lot.

POST https://www.promptbox.cn/api/partial.php

Request

Send a JSON body with the following fields:

Field	Type	Required	Description
`current_price`	number	Yes	Current unit selling price (must be ≥ 0).
`purchase_volume`	number	Yes	Units the customer will purchase (must be > 0 and ≤ `lot_size`).
`lot_cost`	number	Yes	Total cost paid per lot (must be ≥ 0).
`lot_size`	number	Yes	Total units per lot (must be > 0).

Validation rules:

purchase_volume > 0, lot_size > 0, and purchase_volume ≤ lot_size.
current_price ≥ 0, lot_cost ≥ 0.
All fields must be finite numeric values (no NaN/Infinity).

Example request

{
  "current_price": 10,
  "purchase_volume": 50,
  "lot_cost": 200,
  "lot_size": 100
}

cURL

curl -X POST https://www.promptbox.cn/api/partial.php \
  -H "Content-Type: application/json" \
  -d '{
    "current_price": 10,
    "purchase_volume": 50,
    "lot_cost": 200,
    "lot_size": 100
  }'

JavaScript (fetch)

const res = await fetch("https://www.promptbox.cn/api/partial.php", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    current_price: 10,
    purchase_volume: 50,
    lot_cost: 200,
    lot_size: 100
  })
});
const data = await res.json();
console.log(data);

Response

Returns a JSON object containing the echoed inputs, computed outputs, and diagnostics. All numeric values are rounded to 5 decimals.

Top-level structure

{
  "input": { ... },
  "output": { ... },
  "diagnostics": { ... }
}

`output` fields

Field	Type	Description
`subsidy_amount`	number	Dollar amount required to cover unsold units in the lot.
`new_price`	number	Adjusted unit price to fully amortize the lot using the buyer’s partial volume.

Example successful response

{
  "input": {
    "current_price": 10.00000,
    "purchase_volume": 50.00000,
    "lot_cost": 200.00000,
    "lot_size": 100.00000
  },
  "output": {
    "subsidy_amount": 100.00000,
    "new_price": 12.00000
  },
  "diagnostics": {
    "unused_units": 50.00000,
    "utilization_percent": 50.00000,
    "unutilized_percent": 50.00000,
    "notes": [
      "subsidy_amount_equals_cost_of_unsold_units",
      "new_price_equals_current_price_plus_subsidy_per_purchased_unit"
    ]
  }
}

Calculation Logic

Name	Formula	Notes
Unsold units	`unused = lot_size - purchase_volume`	Lower-bounded at 0 by validation.
Subsidy amount	`subsidy = (1 - purchase_volume / lot_size) * lot_cost`	Cost share for units that will never be sold.
New unit price	`new_price = current_price + subsidy / purchase_volume`	Spreads the subsidy across purchased units.
Utilization %	`utilization = (purchase_volume / lot_size) * 100`	Shown in `diagnostics`.

HTTP Status Codes

Status	Meaning	Example body
200	OK — calculation succeeded	See “Example successful response”.
400	Bad Request — validation failed or bad JSON	{ "error": "purchase_volume must be greater than 0." }
405	Method Not Allowed — only POST is supported	{ "error": "Only POST method is allowed." }

Error Cases

Missing field: {"error":"Missing required field: lot_size."}
Non-numeric/NaN/Infinity: {"error":"All fields must be finite numeric values."}
purchase_volume ≤ 0: {"error":"purchase_volume must be greater than 0."}
lot_size ≤ 0: {"error":"lot_size must be greater than 0."}
purchase_volume > lot_size: {"error":"purchase_volume cannot be greater than lot_size."}
Negative current_price/lot_cost: {"error":"current_price cannot be negative."}

Idempotency & Rounding

Deterministic for identical inputs.
All numeric outputs are rounded to 5 decimals to match the original UI behavior.

Rate Limits & Auth

No authentication or explicit rate limiting is documented. Treat as a public unauthenticated endpoint; implement client-side backoff if needed.

Change Log

1.0 — Initial release of the documented API structure and validation behavior.