mbsconvy

Convexity of mortgage pool given yield

Syntax

Convexity = mbsconvy(Yield, Settle, Maturity, IssueDate, GrossRate,
CouponRate, Delay, PrepaySpeed, PrepayMatrix)

Arguments

Yield

Mortgage yield, compounded monthly (in decimal).

Settle

Settlement date. A serial date number or date string. Settle must be earlier than Maturity.

Maturity

Maturity date. A serial date number or date string.

IssueDate

Issue date. A serial date number or date string.

GrossRate

Gross coupon rate (including fees), in decimal.

CouponRate

Net coupon rate, in decimal. Default = GrossRate.

Delay

Delay in days.

PrepaySpeed

(Optional) Relation of the conditional payment rate (CPR) to the benchmark model. Default = 0. Set PrepaySpeed to [] if you input a customized prepayment matrix.

PrepayMatrix

(Optional) Used only when PrepaySpeed is unspecified. Customized prepayment vector. A NaN-padded matrix of size
max(TermRemaining)-by-NMBS. Each column corresponds to each mortgage-backed security, and each row corresponds to each month after settlement.

All inputs (except PrepayMatrix) are number of mortgage-backed securities (NMBS) by 1 vectors.

Description

Convexity = mbsconvy(Yield, Settle, Maturity, IssueDate, GrossRate, CouponRate, Delay, PrepaySpeed, PrepayMatrix) computes mortgage-backed security convexity, given time information, semiannual mortgage yield, and optionally, a prepayment model.

    Note   If you specify the PSA or FHA model, it will be seasoned with how long the debt has been outstanding (the loan's age).

Examples

expand all

Compute the Convexity of a Mortgage Pool Given Yield

This example shows how to compute the convexity of mortgage pool given yield for a mortgage-backed security with the following characteristics.

Yield      = 0.07125;
Settle     = '15-Apr-2002';
Maturity   = '1 Jan 2030';
IssueDate  = '1-Jan-2000';
GrossRate  = 0.08125;
Speed      = 100;
CouponRate = 0.075;
Delay = 14;

Convexity = mbsconvy(Yield, Settle, Maturity, IssueDate, ...
GrossRate, CouponRate, Delay, Speed)
Convexity =

   72.8263

References

[1] PSA Uniform Practices, SF-49

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