## Interpolated Yield Curve (I Curve)

Very seasoned issues: For example, original year bonds with only 5 years to maturity would trade differently from recently issued 5-year bonds. Needless to say, the recently issued 5-year notes are likely to provide more meaningful information, so the old year bonds should be removed. Ad-hoc filters: Some traders remove cheapest-to-delivers; others remove issues trading rich in the repo market. Some additional comments that might be helpful: Most textbooks ask you to interpolate between bond yields, and then bootstrap from that interpolated curve.

That's great for pedagogical purposes, but no one does that in real life. Regarding the dip you mentioned around the year sector, there are two things of note: 1 are you plotting par yields?

Helin Helin 8, 1 1 gold badge 16 16 silver badges 34 34 bronze badges. The gap in years make it impossible to bootstrap without interpolation. I think my opinion would be to keep as many bonds as possible, with each weight as close to unitary as I thought sensible and then analyse the evolution or time series of the residual to the curve of selected bonds. Any opinion? For example, in the US, there's not a ton of value to exclude on-the-runs in recent years For countries like Germany and UK, we really have no choice but to include all issues.

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Post as a guest Name. Email Required, but never shown. Featured on Meta. Tag synonym dashboard 2. We're testing advertisements across the network. It is always linear interpolation that is used to calculate the continuous compounding zero bond rates, irrespective of which interpolation procedure is applied. The units zero bond discounting factors and forward rates describe how par rates and zero coupon rates are calculated in the interest calculation method of the yield curve from interpolated continuous compounding zero bond rates.

If the term of an interest rate that the system is looking for is before the first or after the last grid point, the first or the last grid point is used extrapolation. If the system is looking for an interest date that is between two grid points of the yield curve, either linear interpolation or cubic spline interpolation is used, depending on the interpolation parameter of the yield curve type:.

Linear interpolation calculates a value the system is looking for on the basis of two given values on the line between the two given values.

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P t : interpolated interest rate at time t. P t-1 : lower grid value at time t The number of days is calculated based on the interest calculation method of the yield curve unless continuous compounding zero interpolation is specified. Cubic spline interpolation is used along with linear interpolation to achieve "smoother" yield curves. The yield curve resulting from the cubic spline interpolation retains the feature that in the case of monotonous initial data for example, a normal yield curve , the monotony remains.

The cubic spline interpolation procedure uses parts of third degree polynomials that are linked to the grid points by suitable conditions in such a way that the yield curve is continuously differentiable. Unlike the linear interpolation, in cubic spline interpolation all grid points are included in the calculation of an interpolated value. Cubic spline interpolation provides better interpolation values than linear interpolation.

We present some examples of South African swap and bond curves obtained under the monotone preserving r t t method.

Key words: yield curves, monotone preserving cubic Hermite interpolation, positive forward rate curves, South African swap curve. A yield curve is a plot depicting the spot rate of interest for a continuum of maturities, in some time interval. Yield curves have a number of roles to perform in the functioning of a debt capital market, including:. Akima As noted by Andersen only a limited number of fixed income securities trade in practice, very few of which are zero-coupon bonds.

As such, a model is required to interpolate between adjacent maturities of observable securities, and to extract spot rates from more complicated securities such as coupon bonds, swaps, and Forward Rate Agreements FRAs. As noted by the Bank For International Settlements , such models can broadly be categorised as parametric or spline-based models. Under parametric models, the entire yield curve is explained through a single parametric function, with the parameters typically estimated through the use of some least-squares regression technique.

Important contributions in this field have come from Nelson and Siegel and Svensson As noted by Andersen the resulting fit of such parametric functions to observed security prices is typically too loose for mark-to-market purposes, and may result in highly unstable term structure estimates.

As such, financial institutions involved in the trading of fixed income securities rarely rely on parametric models. Under spline-based models, the yield curve is made up of piecewise polynomials, where the individual segments are joined together continuously at specific points in time called knot points. Such methods involve selecting a set of knot points, extracting the corresponding set of spot rates, and finally interpolating in order to obtain a spot rate function. McCulloch was the first article to suggest modelling the yield curve in such a fashion.

## Interpolation - SAP Documentation

Various methods exist for extracting the set of zero-coupon spot rates corresponding to the chosen set of knot points. Typically, a multivariate optimisation routine is employed whereby the objective is to establish the set of spot rates, which, when combined with an appropriate method of interpolation, produces a yield curve that minimises pricing errors. The problem with this type of approach, however, is that the resulting yield curve is rarely capable of exactly pricing back all of its inputs.

Hagan and West describe an alternative procedure for extracting the set of spot rates which corresponds to the chosen set of knot points. These authors describe a process called bootstrapping, whereby:. The abovementioned iterative procedure will converge to a set of spot rates, which, when combined with a chosen method of interpolation, will produce a curve that exactly prices back all input securities. This bootstrap is a generalisation of the iterative bootstrap discussed in Smit The process of bootstrapping, however, was first described in Fama and Bliss Regardless of how the spot rates corresponding to the chosen set of knot points are extracted, careful consideration has to be given to the chosen method of interpolation.

Both scenarios are unacceptable in a practical framework. Discontinuities in the forward curve imply implausible expectations about future short term interest rates unless the discontinuities occur on or around meetings of monetary authorities , whilst a non-decreasing curve of discount factors implies arbitrage opportunities. Hagan and West introduce the monotone convex method of interpolation, and show that this method is capable of ensuring positive, and mostly continuous forward curves. The monotone convex method does, however, under certain circumstances, produce forward curves with material discontinuities.

In this paper, we present a method for interpolating yield curve data in a manner that ensures positive and continuous forward curves. The objective of this paper is not to introduce a "perfect" method for interpolating yield curve data in fact, our opinion is that such a method does not exist , but rather to present a method that practitioners can use when they require forward curves that are both positive and continuous.

To our knowledge, the method presented in this paper is the only method capable of achieving this feat. In an effort to be consistent with the notation of Hagan and West , we define:. The functions Z t , r t and f t are related through the following equations:. If Z t is not monotone decreasing, then an arbitrage opportunity must exist.

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Under such circumstances, and investor would be able to buy a zero-coupon bond maturing at time t 1 , and simultaneously sell a zero-coupon bond maturing at time t 2 , for an immediate profit of Z. Note, if represents the price of an inflation-linked zero-coupon bond maturing at t , then the abovementioned arbitrage relation would not necessarily hold. Under such circumstances the cash inflows and outflows at and are not known in advance, seeing that they are inflation dependant. Hence, the cash inflow of t 2 - Z t 1 at t 0 would not necessarily constitute a profit.

When interpolating a set of rates that are arbitrage free in the sense that the input set of discount factors are monotone decreasing , it is crucial that our interpolation function preserve this property. McCulloch and Kochin point out that "a discontinuous forward curve implies either implausible expectations about future short-term interest rates, or implausible expectations about holding period returns". Figure 1 can be interpreted as the curve that depicts the evolution of overnight deposit rates under the term structure given in Table 1. Along the entire curve, overnight rates are seen to jump at each of the knot points used to construct the curve.

Clearly, this type of behaviour is implausible, and as such, we should avoid using such curves to value derivative instruments especially instruments that rely on forward curves to project future cash flows. When interpolating yield curve data, we would thus prefer to obtain a continuous forward curve see, for example, Filipovic and James and Webber who also note that consistency with a dynamic term structure model is a desirable feature.

Consider the set of rates r 1 , r 2 , This property should be relaxed when working with real rates. We postulate applying a shape preserving cubic Hermite method of interpolation to the log capitalisation function. For the remainder of this paper, we will refer to this method as the "monotone preserving r t t " method. Consider the interpolant:. Suppose the instantaneous set of forward rates f 1 , f 2 , It can then easily be shown see Hagan and West that:. The problem we face in practice is that the instantaneous forward rates are seldom observable.

We will thus have to rely on an estimation method, and for this purpose, we postulate using a similar method to that proposed by Hagan and West The instantaneous forward rates at the end points, i.